Human Anatomy and Physiology - Cardiovascular System PDF

**[DIPLOMA IN HUMAN ANATOMY AND PHYSIOLOGY]** **[PART 1]** **[MODULE 1: INTRODUCTION TO THE CARDIOVASCULAR SYSTEM]** **After completing this module you will be able to:** - Identify why there is a need for a circulatory system in the human body. - Identify the substances carried to and...

**[DIPLOMA IN HUMAN ANATOMY AND PHYSIOLOGY]** **[PART 1]** **[MODULE 1: INTRODUCTION TO THE CARDIOVASCULAR SYSTEM]** **After completing this module you will be able to:** - Identify why there is a need for a circulatory system in the human body. - Identify the substances carried to and from cells in the body. - List some circulatory systems and briefly describe their components. - Briefly outline the structure and functions of the human cardiovascular system. - Define blood and describe its functions. - List and briefly describe the components of blood. - List the steps involved in response to hemorrhage. - Distinguish between whole blood and plasma transfusions. - Recognise why blood donors and recipients must be matched. **[INTRODUCTION TO THE CARDIOVASCULAR SYSTEM]** **The cardiovascular system is the primary circulatory system of the human body.** It comprises: - **a heart** - **blood** - **blood vessels** **[General Functions of the Cardiovascular System]** One function of the cardiovascular system is **transport. ** Some substances carried by the cardiovascular system are dissolved or suspended in the fluid portion of the blood. Others are bound up in special cellular elements called red blood cells (RBCs). The cardiovascular system also provides **protection** against foreign substances. This function involves active attack by white blood cells as well as more subtle processes of the immune system. **[Direction of Flow of Arteries and Veins]** Blood vessels are the conduits of the cardiovascular system. They make up a closed system, since there is no place in the system where whole blood can leave. **[Arteries]** generally carry blood from the chambers of the heart to the tissue of the body.  **[Veins]** carry blood from the tissues to the chambers of the heart.  (Coronary arteries carry blood from the chambers of the heart inside to the walls of the heart outside.) Arteries and Veins **[The Circulatory System]** Blood circulation is also a** two cycle system**.  It involves both the pulmonary cycle and the **systemic cycle**. Blood circulates through two circuits. In the **pulmonary cycle**, blood circulates from the heart to the lungs and back to the heart.  In the systemic cycle, blood circulates from the heart to the rest of the body and back to the heart. **[Fetal Circulation]** Since the fetus is located within the uterus, its lungs do not take in air.  Therefore, the pulmonary cycle does not function in the fetus. Essentially, fetal blood flows to and from the placenta.  There are certain bypasses in the heart to avoid the pulmonary cycle.  At the time of birth, the fetal circulation is changed to the normal pattern. **[Introduction to Circulatory Systems]** In simple organisms such as unicellular and one or two layer organisms, materials can be transferred among cells by simple processes of **diffusion.** However, in large organisms, a **system** is needed for the distribution and collection of materials. This is because diffusion does not occur fast enough to carry the large volumes of materials necessary through the greater distances required.  Circulatory systems, for example the cardiovascular system, are used by the human body to carry substances **Oxygen** Oxygen is obtained by the blood through the process of external respiration in the lungs. Oxygen is then transported to the individual body cells, where it is used in metabolic oxidation.  This provides energy for production of ATP (adenosine triphosphate), which is necessary for carrying on the life processes of the body. **Nutrients** Some of the substances distributed to the body cells are products of the digestive system.  These materials meet individual cell requirements for energy, growth, repair, synthesis of new materials, and storage for later use. **Waste Substances** Some substances are collected from the body cells for **elimination**.  These include carbon dioxide, nitrogenous wastes, and other potentially harmful substances that are carried to organs like the lungs, liver, or kidneys for elimination from the body. **Hormones** Hormones are the products of endocrine glands.  Hormones and other control substances are distributed throughout the body by circulatory systems. The tissues or organs affected by these substances are usually called target organs. In turn, substances released by the target organs often affect the original endocrine gland. This results in a feedback system. **[Module 2: The Blood Vessel and the Heart]** **After completing this module you will be able to:** - List the types of blood vessel found in the human cardiovascular system, describe their functions and identify their locations. - Briefly describe the structure of arteries, veins and capillaries. - Recognise some special situations associated with the blood vascular system. - Identify the four chambers of the heart. - Briefly describe the structure and function of the heart walls. - Outline the structure and function of the cardiac valves and the chordae tendineae. - Outline how the nerves associated with the heart control heart function. - Briefly describe the blood vessel system which supplies the heart itself. - Outline the structure and functions of the pericardium. - Briefly describe the fibrous skeleton of the heart. - Outline the motive forces which drive arterial and venous blood flow. **[Introduction to the Blood Vessels]** The blood vessels are tubular structures found throughout the entire body.  Since this tubular system is continuous (without interruption or opening), we sometimes refer to it as a **closed system.** In general, there are three types of blood vessels: - Arteries - Veins - Capillaries **Arterioles** and **venules** are small branches of **arteries** and **veins** which connect to **capillaries.** The following abbreviations are used for blood vessels: **A. = artery V. = vein Aa. = arteries Vv. = veins** **[NAVL]** = **Nerve(s)**, **Artery (ies)**, **Vein(s)**, **Lymphatic(s)** **Structure of Blood Vessels** In general, blood vessels have walls composed of three layers. The innermost layer is called the **intima**. It is a simple epithelium made up of a single layer of flat epithelial cells. The main portion of the wall is called the **media**. It is made up of a combination of Fibrous Connective Tissue (FCT) and smooth muscle tissue. The outer surface of the blood vessel is called the **adventitia**. It is an FCT layer. Given an artery and a vein with similar inner diameters, the artery will have a thicker wall than the vein.  This greater thickness is due to the presence of more smooth muscle tissue and the presence of elastic FCT as a significant element in the artery. Capillary walls have only one layer - the **intima**. Capillary networks (beds) are the exchange areas for the cardiovascular system.  This includes the internal exchange areas between the blood and individual cells. Since the capillary wall consists of flat single cells, substances can move readily between the blood and the body cells. **Introduction Blood Supply** There are some special situations associated with blood supply in the cardiovascular system as follows: - Nutrient versus functional blood supply - Collateral circulation - End Arteries - Portal veins **Nutrient vs Functional Blood Supplies**  The** lungs, liver, and heart** actually have two blood supplies.  The **functional** blood supply provides blood to be worked upon by the organ.  The **nutrient** blood supply provides blood through the usual exchange of materials between body cells and the blood. **Collateral Circulation** A **collateral circulation** is a special organization of blood vessels around a major joint or other area of the body. Its purpose is to provide a continuing supply of blood even if one of the vessels is damaged. Several blood vessels are included so that there will be an alternate route when needed. **End Arteries** There are areas of the body where a single artery is the sole supply of blood, such an artery is called an** end artery.** When an end artery is damaged and can no longer supply blood to an area, the tissues of the area will die. End arteries are most common in the **brain and the heart.**  **Portal Veins** The blue in this image indicates the hepatic portal vein A portal vein is a venous blood vessel that begins with capillaries in one area and ends in capillaries of another area.  The most important portal vein in the human body is the **hepatic portal vein.** The hepatic portal vein extends from the capillaries of the digestive system to the capillaries/sinusoids of the liver.  **Introduction to the Location of Blood Vessels**  In the human body, blood vessels are located differently according to their type. View the following table to learn more. +-----------------------------------+-----------------------------------+ | Name | Explanation | +===================================+===================================+ | Arteries | If an artery is injured, the | | | threat to life is greater than | | | with other types of blood | | | vessels.  | | | | | | For protection, arteries tend to | | | be located **deep** within the | | | structures of the body. | | | | | | Only the very smallest of | | | arteries, especially the | | | cutaneous arteries, come close to | | | the surface of the body. | +-----------------------------------+-----------------------------------+ | Veins | Veins can be located at **both | | | deep and cutaneous** levels.  | | | | | | The deep veins accompany the | | | arteries side by side.  | | | | | | The cutaneous veins are found in | | | the subcutaneous (just beneath | | | the skin) layer of the body.  | | | | | | The cutaneous veins drain into | | | the deep veins at specific | | | locations especially the inguinal | | | (groin) region and the axillary | | | (armpit) region. | +-----------------------------------+-----------------------------------+ | Capillaries | The capillaries are | | | located **throughout all | | | tissues** of the body. | | | | | | No individual cell is more than | | | two cells away from a capillary.  | | | | | | The networks of capillaries in | | | the tissues are often | | | called **capillary beds.** | +-----------------------------------+-----------------------------------+ **Introduction to Capillaries** The **capillary beds** make up the greatest cross-sectional area of the cardiovascular system. The exchange of materials between the blood and the cells of the body takes place in the capillary beds. **Capillary Structure** The wall of the capillary consists of a single **layer **of flat cells. The minute spaces surrounding the capillaries and the individual cells of the body make up the tissue space (interstitial/ extracellular space). A Red Blood Cell in a Capillary **Filtration Phenomenon** Fluid passes from the capillary into the tissue space and carries with it various substances. Some of this fluid returns to the capillary on the venous side. **Capillary Sphincters**  The capillary beds are provided with **precapillary sphincters** that can reduce or completely stop the flow of blood into the capillaries.  At the other end of the capillary bed are **postcapillary sphincters**; when these close, there is a back pressure and more fluid flows into the tissue space. **Introduction to the Chambers of the Heart** In humans, the heart is the primary motive force for driving the blood along the arterial vessels.  The heart consists of four separate **chambers**.  Two chambers function as a \"right heart,\" and two function as a \"left heart.\"  The muscular walls (myocardium) of the chambers apply force to the blood within and force the blood to move out of the chambers. +-----------------------------------+-----------------------------------+ | Atrium (Atria) | Description | +===================================+===================================+ | 1\. Right Atrium | **Right Atrium** | | | | | | The two chambers at the top of | | | the heart are | | | called **atria **(singular: | | | atrium). | | | | | | The muscular walls of the atria | | | tend to be relatively thin. | | | | | | Attached to each atrium is an | | | ear-like appendage called an | | | auricle. | | | | | | The auricles of the atria tend to | | | have somewhat thicker walls. | +-----------------------------------+-----------------------------------+ | 2\. Right Ventricle | **Right Ventricle** | | | | | | The two chambers at the bottom of | | | the heart are | | | called **ventricles. ** | | | | | | The right ventricle has a | | | somewhat semi-lunar (half-moon) | | | cross section, since it is | | | wrapped around one side of the | | | left ventricle. | +-----------------------------------+-----------------------------------+ | 3\. Interventricular Septum | **Interventricular Septum** | | | | | | Between the ventricles is a wall | | | of tissue separating the left and | | | right ventricles, this is called | | | the **interventricular septum.** | +-----------------------------------+-----------------------------------+ | 4\. Left Ventricle | **Left Ventricle** | | | | | | The two chambers at the bottom of | | | the heart are called ventricles. | | | | | | The left ventricle tends to be | | | cylindrical in shape. | | | | | | It has relatively thick walls. | +-----------------------------------+-----------------------------------+ | 5\. Interatrial Seuptum | **Interatrial Seuptum** | | | | | | Down the middle of the heart, | | | an **interatrial | | | septum **separates the two atria. | +-----------------------------------+-----------------------------------+ | 6\. Left Atrium | **Left Atrium** | | | | | | The two chambers at the top of | | | the heart are | | | called **atria **(singular: | | | atrium). | +-----------------------------------+-----------------------------------+ **Introduction to Wall Structure** The walls of the chambers of the heart consist of three layers: - The **myocardium   **    - The **endocardium** - The **epicardium**, also known as the visceral pericardium  **Endocardium and Epicardium** The chambers themselves are lined with a simple epithelium known as the **endocardium**. Likewise, the **epicardium** is a simple epithelium tissue. It surrounds the outside of the heart.  **Myocardium** By far the most important of the three layers in the heart walls is the **myocardium**, the middle layer. It is made up of cardiac muscle tissue.  Cardiac Muscle Tissue Cardiac muscle tissue consists of fibers formed by the fusion of many individual cells (syncytium). These cardiac fibers are striated and branched. **Myocardium of Ventricles** The myocardium is **thicker** in the walls of the ventricles than the atria. This is because greater pressures are needed for the ventricles to perform their function. The wall of the left ventricle is especially thick, since it has to drive the blood throughout the body. The inner surfaces of the ventricular walls have ridges of muscle known as the trabeculae carneae, with spaces between them. **Action of the Heart** When the musculature within a chamber wall contracts, the lumen (cavity) decreases in diameter. This is particularly true of the left ventricle. There is also a twisting or wringing action of the left ventricle that causes the apex of the heart to hit against the inner surface of the chest wall - the** apex beat**. **Stroke Volume** The **stroke volume** is the amount of blood forced out of each ventricle in one contraction. The **cardiac output **is the volume of blood pumped out of the ventricles (right into the lungs, left into the systemic circulation) in one minute (expressed in liters per minute). These volumes will change according to the needs of the body. **Introduction to Cardiac Valves** **Valves** are structures that ensure that fluids will pass through them in one direction only. That is, a valve will open to allow fluids to pass in one direction but will close to prevent fluids from passing in the other direction. There are two sets of cardiac valves - the **atrioventricular (AV) valves **and the **semilunar valves**. Although the two sets of valves are quite different in design, they both function passively in response to the flow of the blood.  **The AV Valves** The **AV valves** are found between the atria and the ventricles. The AV valves consist of flaps, known as cusps. The outer margin of each flap is attached to the inner surface of a fibrous ring. The inner edge of each flap is free.  Superior View of the Heart with the Atria Removed On the right side is the **tricuspid valve.** On the left side is the **mitral valve.** (\"Might is never right.\") Thus, the tricuspid valve is between the right atrium and the right ventricle. It is named for its three cusps. The mitral valve is located between the left atrium and the left ventricle. Since it has two cusps, it is sometimes called the **bicuspid valve.** The contraction of the atrial walls forces the blood from the atria through the AV valves and into the ventricles (atrial systole). When the atria relax (atrial diastole) and the ventricles contract,the pressure would tend to drive the blood back into the atria. However, each opening is sealed when the cusps of each AV valve meet in the valve center. This prevents blood from flowing further back into the atria. https://courseware-assets.alison.com/public/published/317/images/image\_65-6931-1489147684978237143.png **Chordae Tendineae** **Chordae tendineae** are a special anatomic arrangement which help prevent the backward flow of blood into the atria. Chordae tendineae are fibrous cords attached to the ventricular side of the cusps. Since these cords of dense **fibrous connective tissue (FCT)** have a fixed length, they cannot be stretched or shortened.  **Papillary Muscles** The other ends of these cords are attached to the** papillary muscles**. The papillary muscles are special extensions of the muscular walls of the ventricles. As the ventricles contract and become smaller, these muscles take up the slack in the cords. https://courseware-assets.alison.com/public/published/317/images/image\_65-6953-1489149207835754769.png **Semilunar (Aortic and Pulmonary Valves)**  Superior View of the Heart with the Atria Removed The bases of the two great arteries (the pulmonary arch and the aortic arch) begin at their respective ventricles as short cylinders of the fibrous skeleton of the heart. Within each of these cylinders are three cuplike cusps, which make up the **pulmonary semilunar valve** and the **aortic semilunar valve**. When the **ventricles contract** (ventricular systole) and the AV valves have closed, the blood moves out into the great arteries through the **aortic and pulmonary semilunar valves. **When the **ventricles relax** (ventricular diastole), the back pressure of the blood in the great arteries forces the cusps of the semilunar valves to the center and seals off each opening. https://courseware-assets.alison.com/public/published/317/images/image\_65-6956-14891495191895246594.png **NAVL of the Heart** The NAVL of the heart are the nerves, arteries, veins and lymphatics which influence the actions of the heart. **Control of Heart** Control of heart functions can be divided into the following areas: - **Extrinsic controls** (control from outside the heart) - **Intrinsic controls **(control from inside the heart)  - **Humoral control,** where some substances transported by the blood can accelerate or slow the action of the heart.  **Extrinsic Controls** A number of cardiac nerves arise from both the sympathetic and parasympathetic portions of the nervous system. (Fibers from the sympathetic portion leave the central nervous system at the thoracic and lumber portions of the spinal cord, while those from the parasympathetic nervous system leave from the brain stem and the sacral region of the spinal cord.) The **sympathetic** portion **accelerates** the action of the heart, while the **parasympathetic** portion **slows** it down.  These portions are both controlled by cardiovascular centers in the medulla of the hind-brainstem. In addition, as everyone is well aware, various emotional states can affect the actions of the heart. The Nervous System The Nervous System **Intrinsic Control** Within the substance of the heart, certain fibers of the myocardium have been transformed from contracting muscle tissue to impulse-transmitting fibers. These fibers provide **intrinsic control** for the action of the heart.  **Sinoatrial (SA) Node** The sinoatrial (SA) node is a collection of impulse conducting fibers in the interatrial septum. The SA node is often called the pacemaker of the heart because it initiates each cycle of the contractions of the heart chambers. **Atrioventricular (AV) node ** The atrioventricular (AV) node is a group of impulse conducting fibers just above the interventricular septum. **Bundle of His and Septal Bundles** Fibers descend from the AV node to form the bundle of His, which branches into the right and left septal bundles. These branches pass down on either side of the interventricular septum. **Purkinje Fibers** The septal bundles connect with the Purkinje fibers located throughout the ventricular walls. **Intrinsic Controls** Impulses begin in the SA node, pass to the AV node, and then descend through the septal bundles and on to the purkinje fibers to stimulate the myocardium of the ventricular walls to contract. **Coronary Arteries** **Functional and Nutrient Blood** Blood flows through the chambers of the heart. This blood, upon which the heart acts, is called** functional blood.  **The blood which supplies the heart tissue itself is called** nutrient blood.** This blood supplies oxygen and food materials and removes waste materials.  This nutrient blood is supplied to the walls of the heart by the right and left coronary arteries. **Valves** The openings leading into the coronary arteries are located in the base of the ascending aorta, just above the **semilunar valve (aortic valve)**. When this valve is open, its cusps cover the openings of the coronary arteries. When the valve is closed, the back pressure of the blood in the aorta fills the coronary arteries with blood. The coronary arteries then distribute the blood to all of the tissues of the relaxed heart. **End Artery** Many of the branches of the coronary arteries are of the **end artery type. **This means that such a branch is the sole supply of nutrient blood to a specific area of the heart. If the branch should be closed for any reason, the tissue in that area will die due to lack of oxygen and nourishment. **Cardiac Veins, Coronary Sinus and Thebesian Veins** The blood from the tissues of the heart is collected by the **cardiac veins.** These veins empty into the **coronary sinus**, a vessel, which in turn empties into the right atrium. The **thebesian veins** are many minute sinuses found in the myocardium of the ventricles. They extend from the lumen into the myocardium of each ventricle.  Cardiac Veins **Introduction to the Fibrous Skeleton of the Heart** Traverse section of the heart showing the fibrous rings around the valves. Traverse section of the heart showing the fibrous rings around the valves. There is a fibrous connective tissue (FCT) structure **within **the substance of the heart. This structure is known as the** fibrous skeleton** of the heart. **To learn more about the fibrous skeleton of the heart parts:** **Fibrous Skeleton** The fibrous skeleton of the heart serves two general purposes: As sites of attachment for muscle tissues As supporting structures for the cardiac valves **Fibrous Structures** All of the fibrous structures are continuous and form the fibrous skeleton of the heart. However they can be divided into three parts as follows: The fibrous portion of the interventricular septum The atrioventricular (AV) rings Cylinders at the bases of the great arteries **Fibrous Portion of the Interventricular Septum** The uppermost portion (also called the membranous portion if the **interventricular septum **is part of the fibrous skeleton of the heart. **Atrioventricular Rings** Each **atrioventricular valve **of the heart is surrounded by a dense fibrous ring. This ring maintains the valve openings. **Cylinders at Bases of Great Arteries** Each of the **semilunar valves **of the heart is located within a short, fibrous cylinder. This cylinder maintains the structure and function of the valve. **The Pericardium** The heart is an active organ of the human body. Its pumping action, which begins in the very early embryo, continues without stopping until death. During each cycle of its activity, the heart changes in shape and size and tends also to rotate. (The number of cycles per minute is called heart rate.) To reduce the amount of friction resulting from this activity, the heart is contained within a serous (secretory) sac, called the **pericardium**, or pericardial sac.  **1 - Fibrous Pericardium** The **fibrous pericardium** is a very dense fibrous envelope. This envelope forms the outer portion of the pericardial sac. **2 - Parietal Pericardium** The **parietal pericardium** is the outer serous membrane. **3 - Serous Space** Between the two serous pericardia is a very **thin space** containing a thin film of pericardial fluid. This lubricating fluid makes the action of the heart much less strenuous. **4 - Visceral Pericardium** The visceral pericardium intimately covers the surface of the heart. This is also referred to as the epicardium. **Introduction to Blood Flow** The blood is driven through the blood vessels by a variety of motive forces. Blood flow takes place in: **arteries and veins** Blood is driven through the arteries by a combination of forces as follows: - the force produced by the contraction of the ventricular walls - the elastic recoil of the arterial walls - vasoconstriction - gravity https://courseware-assets.alison.com/public/published/317/images/image\_65-6401-14889935291522948443.png **Systole** When the left ventricle contracts - **systole**, it forces the blood into the aortic arch. Above the base cylinder, the wall of the aortic arch is mainly elastic FCT. As the blood fills the aortic arch, the walls are stretched.  **Vasoconstriction and Gravity** https://courseware-assets.alison.com/public/published/317/images/image\_65-6401-14889935291522948443.png **Vasoconstriction** is the actual contraction of the arterial walls. Vasoconstriction can further increase the pressure on the blood in the arteries. **Gravity** helps to move blood to the trunk and lower members. However, it is a hindrance in moving blood to the head and neck. **Venous Blood Flow** Blood is driven through the veins by a combination of forces as follows: - the venous valves - pressure from the arteries - pressure from muscular contractions - gravity There is usually a low level of pressure in the veins. There are valves in the veins that ensure that blood flows continuously toward the heart. Therefore, as pressure is applied to a vein, there will be a pump effect.  Venous Valve **Pressure from Arteries and Muscular Contractions** The muscular compartments of the upper and lower limbs tend to be full in healthy persons. Therefore, as blood enters the** arteries** within these compartments, a volume of blood must leave through the veins. During** muscular activity**, additional forces press against the veins and produce a \"milking action.\" Again, blood moves through the veins back toward the heart. **Gravity** In the head and neck, **gravity** helps to move the blood down through the veins. In the trunk and lower limbs, the **valves** help to prevent a backward flow of blood in the veins. **Overview of Blood Flow** https://courseware-assets.alison.com/public/published/317/images/image\_65-6993-14939074311897093987.png Lesson Summary **The main points from this module are as follows:** - In general, there are three types of blood vessels - arteries, veins, and capillaries. - Blood vessels are generally composed of three layers - the intima, the media and the adventitia. - For protection, arteries tend to be located deep within the structures of the body. - Veins can be located at both deep and cutaneous levels.  - The capillaries are located throughout all tissues of the body. - The exchange of materials between the blood and the cells of the body takes place in the capillary beds. **Some special situations which arise in the blood vascular system include:** - nutrient versus functional blood supply - collateral circulation - end arteries - portal veins The heart comprises two upper chambers - the atria - and two lower chambers - the ventricles The walls of the chambers of the heart consist of three layers - the endocardium, the epicardium and the myocardium. There are two sets of cardiac valves the atrioventricular (AV) valves and the semilunar valves. The fibrous skeleton of the heart provides sites of attachment for muscle tissues and supporting structures for the cardiac valves. The heart is enclosed in a protective sac called the pericardium. Heart function is governed by extrinsic controls, intrinsic controls and humoral control. Blood is supplied to the heart by the coronary arteries, cardiac veins, coronary sinus and thebesian veins. Arterial blood flow is driven by the contraction of the ventricular walls, the elastic recoil of the arterial walls, vasoconstriction and gravity. Venous blood flow is driven by the pump effect from venous valves, pressure from arteries, pressure from muscular contractions and gravity. **[MODULE 3: INTRODUCTION TO THE HUMAN DIGESTIVE SYSTEM]** **After completing this module you will be able to:** - Describe the human digestive system. - Explain how energy is obtained from food. - List the stages involved in the digestion process. - List the three main food types. - Describe vitamins. - Describe ingestion. - Explain each stage of the process of swallowing. - Describe the structure and functions of the stomach. **The Energy Cycle** **Solar Radiation** The ultimate source of all energy for living things on Earth is the Sun. This energy reaches the Earth in the form of solar radiation. **Photosynthesis** The energy from solar radiation is stored by plants in the chemical bonds of glucose molecules. The process for doing this is called **photosynthesis**. https://courseware-assets.alison.com/public/published/317/images/image\_65-7052-14891580911898962956.png **PHOTO = light   SYNTHESIS = put together** Photosynthesis takes place in the presence of a green substance called **chlorophyll**.  **Food Consumption** The green plants are then utilized as food by various animals. Ultimately, either the green plants or the animals that ate the green plants are consumed by humans. https://courseware-assets.alison.com/public/published/317/images/image\_65-7057-14891583441501077618.png **Digestive and Circulatory Systems** The glucose is released through the processes of digestion. It is then delivered to the cells of the body by the circulatory system.  **Metabolic Oxidation** Within the cells of the body, the energy is released from the glucose by the chemical process known as metabolic oxidation. https://courseware-assets.alison.com/public/published/317/images/image\_65-7057-14891601011933822322.png **Production ATP** The released energy is then used to produce the compound known as ATP (adenosine triphosphate).  https://courseware-assets.alison.com/public/published/317/images/image\_65-7059-14891587571119475890.png Metabolic oxidation and the production of ATP occur in the **mitochondria.** For this reason, the mitochondria are known as the \"powerhouses\" of the cell. When** energy is required** for carrying on any of the life processes, it is obtained from the ATP.  **Introduction to Food** A food is any substance utilized by a living thing for energy, growth and repair. There are both plant and animal sources for foods. For example, you can eat grains in the form of bread, and you can eat the meat of an animal that ate such grains. In general, nutrients in food fall into three categories.  View the following table to learn more. +-----------------------------------+-----------------------------------+ | Nutrients | Description | +===================================+===================================+ | Carbohydrates | Starches and sugars | +-----------------------------------+-----------------------------------+ | Lipids | Fats and oils | | | | |  | | +-----------------------------------+-----------------------------------+ | Proteins | Meat | +-----------------------------------+-----------------------------------+ **Vitamins, Minerals and Water** **View the following table to learn about the other nutrients required by the human body.** +-----------------------------------+-----------------------------------+ | Nutrients | Description | +===================================+===================================+ | Vitamins | For example, peppers contain | | | vitamin C | |  | | +-----------------------------------+-----------------------------------+ | Water | | +-----------------------------------+-----------------------------------+ | Minerals | For example, peanuts contain | | | zinc. | |  | | +-----------------------------------+-----------------------------------+ **Vitamins** **Vitamins** are a group of chemicals that are required in very small quantities for the proper functioning of the body. Vitamins are found in varying amounts in different foods. In fact, many processed foods contain artificial vitamin supplements. Vitamins are covered in more detail in the next unit. **Vitamins** Vitamins can be considered in two major categories: **   water-soluble vitamins** **   fat-soluble vitamins** The water-soluble vitamins include vitamin C, B-complex vitamins, Folic acid and Nicotinic acid. There is a daily requirement for water-soluble vitamins as they are excreted continuously in urine. On the other hand, fat-soluble vitamins can be accumulated in the fat of the body. These include vitamins A, D, K and E. **View the following table to learn more about vitamins.** +-----------------------------------+-----------------------------------+ | Vitamins | Description | +===================================+===================================+ | Vitamin B1 | Water-soluble vitamin B1 | | | (thiamine hydrochloride0 is | |  | | +-----------------------------------+-----------------------------------+ | Vitamin B2 | Water-soluble vitamin B2 | | | (riboflavin) is found in milk, | | https://courseware-assets.alison. | milk products, leafy green | | com/public/published/317/images/i | vegetables, fruit, and liver. | | mage\_65-7088-1489162032204742446 | | | 5.png | | +-----------------------------------+-----------------------------------+ | Vitamin B6 | Water-soluble vitamin B6 | | | (pyridoxine hydrochloride) is | |  | | +-----------------------------------+-----------------------------------+ | Nicotinic Acid | Water-soluble nicotinic Acid | | | (niacin) and nicotinamide | | | (niacinamide) are present in | | | meat, liver, milk, peanuts, and | | | whole grain cereals. | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | Vitamin B12 | Water-soluble vitamin B12 is | | | found in liver, milk, eggs, and | | | cheese. | +===================================+===================================+ | Folic Acid | Water-soluble folic acid is found | | | in leafy green vegetables and | | https://courseware-assets.alison. | liver. | | com/public/published/317/images/i | | | mage\_65-7092-1489162279150876218 | | | 5.png | | +-----------------------------------+-----------------------------------+ | Vitamin C | Water-soluble vitamin C (ascorbic | | | acid) is found in citrus fruits, | |  | | +-----------------------------------+-----------------------------------+ | Vitamin A | Fat-soluble vitamin A (retinol, | | | retinal, carotenoids) is mainly | | https://courseware-assets.alison. | obtained from yellow-colored | | com/public/published/317/images/i | vegetables of all sorts (for | | mage\_65-7092-1489162370146662400 | example, carrots and squash.) | | 6.png | | +-----------------------------------+-----------------------------------+ | Vitamin D | Fat-soluble vitamin D | | | (cholecalciferol) is produced in | |  | It is also present in fish liver | | | oils, butter, and egg yolk. | +-----------------------------------+-----------------------------------+ | Vitamin K | Vitamin K occurs in such foods as | | | alfalfa, spinach, cabbage, and | | | egg yolk. | | | | | | Fat-soluble vitamin K | | | (phylloquinone, menaquinone) is | | | important in blood clotting. | | | | | | It is actually produced by | | | microorganisms located in the | | | large intestines. The source of | | | vitamin K may be lost during the | | | administration of antibiotics. | +-----------------------------------+-----------------------------------+ | Vitamin E | Vitamin E is found in nuts, seeds | | | and vegetable oils. | |  | | | | Fat-soluble vitamin E\'s | | | (tocopherols, tocotrienols) | | | functions in humans is not | | | known.  | | | | | | Research indicates that vitamin E | | | has important functions in | | | various species, but the specific | | | function varies from species to | | | species. | +-----------------------------------+-----------------------------------+ **The Human Digestive System** The overall function of the human digestive system is to provide materials to be used by the individual cells of the body. These materials are used by the cells as **energy **for life processes for **growth and repair** of the body tissues. The following processes are involved in the human digestive system: - Ingestion (taking in) of foods - Initial processing - Storage - Digestion - Absorption - Elimination of unused materials **View the following table to learn more about the human digestive system.** https://courseware-assets.alison.com/public/published/317/images/image\_65-7038-14891572511256300671.png +-----------------------------------+-----------------------------------+ | Name | Function | +===================================+===================================+ | 1\. Mouth, Pharynx and Salivary | The functions of the **mouth, | | Glands | pharynx and salivary | | | glands** include: | | | | | |  ingestion and chewing of food | | | | | |  initiation of swallowing | | | reflex | | | | | |  moistening of food | | | | | |  partial digestion of food | | | using the amylase enzyme | +-----------------------------------+-----------------------------------+ | 2\. Esophagus | The **esophagus** provides the | | | pathway for food to reach the | | | stomach. It functions include: | | | | | |  movement of food to the | | | stomach by peristaltic waves | | | | | |  lubrication | +-----------------------------------+-----------------------------------+ | 3\. Liver | The **liver** is a large organ | | | located in the upper right part | | | of the abdomen. Its functions | | | include: | | | | | |  the secretion of bile used by | | | the small intestine in the | | | digestive process; this includes | | | bile salts needed to increase the | | | solubility of fats | | | | | |  many other non-digestive | | | functions | +-----------------------------------+-----------------------------------+ | 4\. Gall bladder | Between meals the **gall | | | bladder** stores bile which has | | | been secreted by the liver. | +-----------------------------------+-----------------------------------+ | 5\. Pancreas | The **pancreas** is an elongated | | | gland located behind the | | | stomach. It secretes digestive | | | enzymes into the small intestine. | +-----------------------------------+-----------------------------------+ | 6\. Stomach | The **stomach **is a sac-like | | | organ located between the | | | esophagus and the small | | | intestine. Its functions include: | | | | | |  storing, dissolving and mixing | | | food | | | | | |  partial digestion of food | | | | | |  regulation of emptying of | | | dissolved food into the small | | | intestine | +-----------------------------------+-----------------------------------+ | 7\. Large Intestine | The functions of the **large | | | intestine** include: | | | | | |  temporary storage of undigested | | | material | | | | | |  absorption of some salt and | | | water  | | | | | |  mixing and propulsion of | | | contents  | | | | | |  defecation | +-----------------------------------+-----------------------------------+ | 8\. Small Intestine | The small intestine is a long | | | tube that leads from the stomach | | | to the large intestine. It\'s | | | functions include: | | | | | |  the final stage of digestion | | | | | |  absorption of most substances | +-----------------------------------+-----------------------------------+ **Hunger** When an individual needs food, he experiences a sensation known as hunger. The **hypothalamus** area of the brain controls the degree of hunger or satiation (feeling of being well fed). To do this, the hypothalamus receives various types of information from throughout the body.  **Food Selection** When food is presented, an individual goes through a process of food selection. He or she has a greater appetite for some foods than others. This process is related both to previous learning and to current, internal chemical requirements. https://courseware-assets.alison.com/public/published/317/images/image\_65-7103-14891632601816904832.png **Biting** Together, the upper and lower incisors (anterior teeth) create two cutting surfaces like a pair of scissors.  As food items are placed in the opening of the oral cavity, bite-size chunks of food are cut off. These chunks are usually just the right size for the mouth to handle. https://courseware-assets.alison.com/public/published/317/images/image\_65-7105-14891633271591790617.png **Two Key Facts about Digestion** In general terms, there are two key facts to understand about digestion: 1. First, digestion is a chemical process. Through a process called hydrolysis, food is broken down into its constituent parts. 2. Second, this chemical process takes place only at wet surfaces of the food. **Mastication** During the process known as **mastication** (chewing), the food particles are gradually broken down into smaller and smaller pieces. At the same time, the total surface area of the food increases greatly. This grinding and crushing of the food particles are accomplished by the posterior teeth, the **premolar** and **molar** teeth. For this purpose, these teeth have broad, opposing surfaces.  **Saliva** The **salivary glands** and the **buccal glands** secrete fluids into the oral cavity.  The buccal glands are serous and mucous glands on the inner surfaces of the cheeks. There are three pairs of salivary glands in the head. The fluids secreted by all of these glandular structures are collectively known as the saliva. This **saliva**, which contains mucus, moistens and lubricates the surface areas of the food particles produced by mastication. In addition, saliva also dissolves some of the molecules of the food items. **Taste Buds** **Taste buds** sample the dissolved food molecules and test the quality of the food being eaten. Taste buds are located on the tongue and the back of the oral cavity. The mucus in the saliva tends to hold the food particles together as a bolus. Since the mucus also makes this bolus somewhat slippery, it can slide readily through the initial portion of the digestive tract. https://courseware-assets.alison.com/public/published/317/images/image\_65-7112-14891637431614661537.png **Introduction to Swallowing**  When food has been adequately broken down (increased surface area), wetted thoroughly, and tested (tasted), it is ready to be swallowed. The bolus is moved posteriorly out of the mouth (oral cavity) into the pharynx and then down through the esophagus to the stomach. The pharynx is common to both the digestive and respiratory systems. Therefore, as the bolus passes through the pharynx, both the upper and lower air passageways must be protected. Otherwise, food particles might enter the passageways. Click on the numbers below to see the steps involved in swallowing food. **Movement Out of the Oral Cavity** https://courseware-assets.alison.com/public/published/317/images/image\_65-7116-1489164056714910119.png **Movement out of the oral cavity involves:** **Initial Movement of the Bolus:**  There are intrinsic muscles in the tongue. Through their action, the tongue arches upward and presses against the hard palate, the roof of the mouth. This initiates the posterior movement of the bolus. **Action of the Hyoid Complex:** The muscles of the hyoid bone pull the hyoid bone upward and force the tongue upward into the oral cavity. This closes up the front part of the oral cavity and forces the bolus further to the rear. **Action of the Soft Palate:** As the bolus approaches the pharynx, the soft palate is raised. Thus, the soft palate serves as a trap door to close the upper air passageway. By tensing to resist the pressure from the bolus of food, the soft palate ensures the continued backward movement of the bolus into the pharynx. **Movement through the Esophagus** The **esophagus** is a tube with muscular walls. It extends from the pharynx above, through the neck and thorax, to the stomach in the abdomen. Wavelike contractions (peristalsis) move the bolus through the esophagus to the stomach.  **Introduction to the Stomach** The **stomach **is a saclike enlargement of the digestive tract. Food that has been processed in the oral cavity is received by the stomach via the esophagus. The stomach\'s capacity is great enough to allow the individual to take in enough food material at one time to last for an extended period of time. This allows the individual to engage in activities other than eating. https://courseware-assets.alison.com/public/published/317/images/image\_65-7165-14913086342114712284.jpeg In addition, certain digestive processes are initiated in the stomach. The food is retained in the stomach for varying lengths of time, depending upon the types of food eaten, the condition of the individual, and many other factors. **Adaptations of the Stomach for the Storage Function** The stomach is adapted as a storage area in several ways. Its wall is quite stretchable. The mucosal lining of the stomach is thrown up into longitudinal folds called **rugae**. These rugae flatten out as the stomach capacity increases.  There are valves at each end of the stomach. The gastroesophageal valve is located at the point where the esophagus enters the stomach. The well-developed **pylorus** or** pyloric valve **separates the stomach from the small intestine. **Stomach Adaptations for Additional Food Processing** The mucosal lining of the stomach contains a number of **gastric glands.** These gastric glands produce gastric digestive juices for initiating digestion, particularly of **proteins.** Some of the gastric glands also produce **hydrochloric acid**. Thus,** chyme**, the mixture produced by the stomach, is quite acidic.  **Musculature of the Stomach**  The stomach has three layers of muscle: - An outer longitudinal layer, - A middle circular layer, - An inner oblique layer. These three layers of muscle enable the stomach to mix its contents thoroughly. **The main points from this module are as follows:** The function of the human digestive system is to provide materials for** energy, growth and repair**. The following processes are involved in the human digestive system: - Ingestion - Initial processing - Storage - Digestion - Absorption - Elimination - In general, food can be divided into three categories: **carbohydrates, lipids, and proteins.** - Other necessary nutrients include: **Water, vitamins, and minerals.** - **Food sources for fat soluble vitamins:**  - Food sources for the** water** soluble vitamins: https://courseware-assets.alison.com/public/published/317/images/image\_65-7142-14891663681755782765.png  The initial breakdown of food takes place in the oral cavity, where food is chewed, and some of it is dissolved in **saliva.** **Swallowing** can be divided into three phases as follows: - movement of food out of the oral cavity - movement of food through the pharynx - movement of food through the esophagus The **epiglottis** is a thin flap of cartilage which folds over the entrance to the larynx during swallowing thus preventing food from entering the trachea. The** stomach** provides temporary storage for food and it initiates certain digestive processes, for example it begins the breakdown of proteins. **[MODULE 4: DIGESTION, ABSORPTION, ELIMINATION AND PROTECTION]** **After completing this module you will be able to:** - Briefly describe how food is digested in the human body. - Explain how nutrients are absorbed into the human body. - Briefly describe how waste materials are eliminated from the human. - Briefly describe the protection mechanisms of the digestive system. - Explain how the mammary gland provides protection from infection, for a baby, during breast feeding. **Introduction to Digestion** **Digestion** involves the breakdown of foodstuffs into their basic constituents. The small intestine is the primary area of the body for digestion of foodstuffs. The end-products (molecules or particles) of digestion are small enough to be absorbed through the walls of the small intestines. These end-products are then distributed throughout the body by the circulatory systems. https://courseware-assets.alison.com/public/published/317/images/image\_65-6527-14890571741706218.png **Digestion as a Chemical Process** Digestion is a chemical process. In general, chemical processes are expected to occur at a rate proportional to the temperature. However, in the human body, the temperature is not high enough for the chemical process of digestion to produce a sufficient quantity of the materials needed. Therefore,** digestive enzymes** are present to maintain the appropriate rates of reaction.   **Digestive Enzymes** **Digestive enzymes **are catalysts.  A catalyst is a substance that improves the rate of a reaction without being consumed itself. The molecule upon which an enzyme acts is called a substrate. Because of digestive enzymes, digestion proceeds at a pace fast enough to provide the materials needed by the body. **Foodstuff** **Enzyme** **End Product** --------------- ------------ ----------------- Carbohydrate Amylases Simple sugars Lipid Lipases Fatty acid Protein Proteases Amino acids  **Digestion in the Mouth and Stomach** The digestive process begins in the oral cavity. The saliva contains enzymes which initiate the digestion of complex carbohydrates. In the stomach, the gastric glands produce enzymes that initiate the digestion of proteins. \ **Digestion in the Small Intestine** The majority of digestion in humans takes place in the **small intestine.** The small intestine is located in the central part of the abdomen, immediately beneath the abdominal wall. In healthy individuals, a flap called the greater omentum is draped over the small intestine (between it and the anterior abdominal wall). The greater omentum has a great deal of fat for insulation. It is richly supplied with blood vessels for heat. In fact, the greater omentum is sometimes compared to an \"electric blanket\" for the small intestine. **Digestive Enzymes in the Small Intestine** In the small intestines, there are digestive enzymes for all three classes of foodstuffs - carbohydrates, lipids, and proteins. Enzymes for completing the digestion of these three classes are found in the fluids produced by the **pancreas **and glands in the mucosa of the small intestines.  Moreover, there is a fluid called** bile** that is produced by the **liver** and stored in the gallbladder for release into the small intestines. Bile helps in the digestion of lipids. The secretions from the liver and pancreas flow into the duodenum which is the first section of the small intestine. **The Small Intestine** The small intestine in adults is a long and narrow tube about 7 meters (23 feet) long. The time it takes for material to travel from beginning to end is just right for the completion of digestion. **Absorption** The end-products of digestion are absorbed primarily through the walls of the small intestine. **Surface Area** The amount of absorption is proportional to the surface area of the walls which contact the contents. Two anatomical specializations serve to increase the surface area of the small intestine: - There are permanent circular folds (plicae circulares) in the mucosal lining of the small intestines. - The entire inner surface of the mucosa is covered with** villi**.  https://courseware-assets.alison.com/public/published/317/images/image\_65-7167-1491308753872930851.jpeg Micrograph of Intestine Wall **Villi **are minute, fingerlike processes that extend into the lumen (cavity) of the small intestines. Capillaries in the villi enable the absorption of nutrients from the small intestine into the blood stream. **Hepatic Venous Portal System** All of the blood capillaries in the absorptive areas of the digestive tract join to form the **hepatic portal venous system. **A venous portal system is a system that begins in capillaries, which join to form veins, which in turn end in another group of capillaries. The hepatic portal vein carries the blood from the absorptive areas of the digestive system to the liver. **The Liver** The liver performs a number of actions on the blood. Excess materials are removed and stored. For example, some glucose is stored as glycogen. Toxic materials are degraded, and microorganisms are removed. The \"treated\" blood is then routed from the liver to the heart and then throughout the body. **Utlization of Lipids** \ The **lipid **materials, such as fatty acids and glycerol, are carried to the venous system beyond the liver. Lipid materials are a high energy source. They are stored as fat throughout the body so that they will be available when needed for energy. Body fat serves as **insulation** in the subcutaneous tissues. It also gives **buoyancy** to the body in water. **Cholesterol** is a very important substance in the body. It participates in the functioning of the liver and in other activities of the body. However, there are certain medical conditions in which physicians prescribe a low-cholesterol and/or low-fat diet. **Elimination** A number of substances within food materials cannot be digested by the human digestive system. For example, **cellulose**, a complex carbohydrate found in plants, is indigestible to humans. Cellulose is commonly referred to as \"bulk\" or \"fiber\". Also when individuals consume great quantities of foods, some will not be digested.  Both undigested and indigestible material passes out of the small intestine into the **large intestine (colon)** through the** ileocecal valve**. **Consolidation of Contents** In the large intestine, the fluid mass, which came from the small intestine, is gradually consolidated into a semisolid mass called **feces.** **Salvage **is a major function of the large intestine. Water is the primary item which is salvaged. Also some previously unabsorbed end products of digestion are absorbed from the large intestine. At the same time certain excretions from the body are deposited in the fecal mass. **Mucus** As the contents increase in solidity,** mucus** is added to facilitate their movement through the large intestine. (Previously, we have seen the addition of mucus to the bolus in the mouth to facilitate movement.) This mucus is produced by unicellular glands in the mucosal lining of the large intestine.  Because of their microscopic appearance, these unicellular glands are called **goblet cells**, seen here in a micrograph of the large intestine wall. https://courseware-assets.alison.com/public/published/317/images/image\_65-7197-1489399321983635674.png **Microorganisms** Many **microorganisms** are found within the lumen or cavity of the large intestine. Certain microorganisms are responsible for the production of vitamin K. Depending on the type of food present, some species of microorganisms produce various gases (flatulence). On occasion, pathogenic organisms may be present and may cause illness. **Storage of Feces and Elimination** Toward the lower end of the large intestine, the contents (feces) have become relatively consolidated. This consolidated mass is retained (stored) mainly in the** rectum** and the lower portion of the** large intestine.** At the appropriate time, the feces is passed out of the body (defecation). The feces passes through the **anal canal **and **anus**. This is accomplished by the relaxation of the anal sphincter muscles. **Elimination** At the appropriate time, the feces is passed out of the body (defecation). The feces passes through the **anal canal** and **anus**. This is accomplished by the relaxation of the anal sphincter muscles. **The Reticuloendothelial System** The human digestive system is essentially a continuous tube, which is open at both ends - the mouth and the anus. Therefore, the lumen (cavity) connects directly with the surrounding environment, and a variety of toxic materials and/or microorganisms may be ingested with foods. Special mechanisms are associated with the human digestive system to provide protection. Such protective mechanisms are said to belong to the **reticuloendothelial system**. This term refers to the association of such mechanisms with a particular layer of epithelial cells. **Lymphoid Tissue** The** lymphoid tissues** are a primary component of the reticuloendothelial system. The lymphocyte is an important type of white blood cell that is also found in the interspaces of lymphoid (or lymphatic) tissues. Lymphocytes signal other types of white blood cells to phagocytize (engulf) foreign materials found within the body. The lymphoid tissues are particularly important in individuals from birth until about 15 years of age. The mass of lymphoid tissue found in the body of a 12-year-old is about twice the mass found in a full-grown adult.  Between 6 and 15 years of age, the immune system of the blood becomes the primary protector of the body from disease. **\"Tonsils\" of Small Intestine** Lymphoid aggregates of varying size are found in the walls of the small intestine. In the ileum portion, in particular, these aggregates are large enough to be easily observed and are called **Peyer\'s patches. ** These might be considered \"tonsils\" of the small intestines.  \ A structure known as the **vermiform appendix** is located at the beginning of the large intestine, at the inferior end of the cecum. Since the vermiform appendix is actually a collection of lymphoid tissue, it should be considered the \"tonsil\" of the large intestine. **Kupffer\'s Cells** As we have seen, blood from the absorptive areas of the gut tract is collected and delivered to the liver by the hepatic venous portal system. As this blood passes through the sinusoids (channels) of the liver, it is acted upon by cells called** Kupffer\'s cells. **These cells line the sinusoids. Since Kupffer\'s cells remove harmful substances from the blood, they are considered to be part of the reticuloendothelial system. **The Mammary Glands** When a newborn baby is nursed by its mother, the initial secretion of the mammary glands is called **colostrum. **Although this colostrum lacks nutrients, it is loaded with **antibodies.** These antibodies provide the infant with its primary protection for the first 6 months of life. After a few days, the mammary gland produces the natural food for the human infant. As the infant suckles at the mother\'s breast, there is a certain amount of reflux (backward flow) into the milk ducts of the mammary gland. Should the infant develop an upper respiratory infection, the organisms causing the infection will be included in this reflux. Generally by the next time the infant suckles, the mammary gland will have produced the appropriate antibodies. These antibodies are delivered to the infant for its protection. **The main points from this module are as follows:** **Area of the Body** **Enzyme** **Foodstuff Digested** ---------------------- ------------------- ------------------------ Mouth Amylases Carbohydrates Stomach Protein digesting Protein Small intestine Many enzymes All types - The small intestine is the primary area of the body for the digestion of foodstuffs. - Enzymes are used to speed up the process of digestion. - Most of the end products of digestion are absorbed from the small intestine into the hepatic portal venous system. - Blood coming from the hepatic portal venous system is \"treated\" by the liver before being sent to the heart for circulation. - Water and any previously unabsorbed digestive end products are absorbed from the large intestine into the blood. - Waste materials from the digestive process are eliminated from the large intestine, through the anus, in the form of feces. - The reticuloendothelial system provides protection in the digestive system. - It encompasses lymphoid tissue in the tonsils, small and large intestine, and the Kupffer cells in the liver. - After the birth of a baby, colostrum, the initial secretion from the mammary glands, is filled with antibodies. - The mammary glands respond to infection, in reflux from the feeding baby, by producing the appropriate antibodies.