Biology Chapter 8: Circulatory System

Introduction to the Circulatory System

Circulatory systems deliver nutrients, oxygen, hormones, and waste products throughout the body.
Blood, lymph, and tissue fluid are the main circulating fluids in humans.
The human circulatory system is a closed system, contrasting with open systems seen in organisms like insects.

Blood Overview

Blood is a fluid connective tissue with multiple functions beyond transport.
An average adult has approximately 5-6 liters of blood.
Blood has a normal pH range of 7.3 to 7.45, making it slightly alkaline.

Blood Composition

Blood consists of plasma (55-60%) and cellular components (40-45%).
Plasma is primarily 90-92% water, contains proteins (7-8%), inorganic salts, and other substances.
The primary cellular components are red blood cells (RBCs), white blood cells (WBCs), and platelets.

Functions of Blood

Transport: Delivers nutrients, oxygen, carbon dioxide, waste products, and hormones throughout the body.
Protection: Clotting prevents blood loss and white blood cells combat pathogens.

Blood Clotting

Clotting involves platelets releasing thrombokinase to convert prothrombin to thrombin, which processes fibrinogen into fibrin, forming a mesh to stop bleeding.
Proper clotting requires a sufficient platelet count; decreased levels lead to increased hemorrhage risk.

Blood Group Systems and Transfusion

Blood groups are determined by antigens on the surface of RBCs, primarily the ABO system (A, B, AB, O).
O blood type is universal donor; AB is universal recipient, allowing for broad compatibility during transfusions.
Matching donor and recipient blood types is crucial for safe transfusions.

Blood Vessels

Blood vessels include arteries, veins, and capillaries.
Arteries carry oxygen-rich blood away from the heart, while veins return oxygen-poor blood.

Heart Structure and Function

The heart has four chambers: two atria and two ventricles.
The sino-atrial node (SAN) functions as the heart's pacemaker, regulating heart rate.
Each cardiac cycle consists of contraction and relaxation phases, corresponding to a heartbeat.

Circulatory Pathways

Pulmonary circulation transports blood between the heart and lungs for oxygenation.
Systemic circulation carries oxygenated blood from the heart to the rest of the body.
The hepatic portal system manages blood flow from the digestive organs to the liver.

Lymphatic System

Complementary to the circulatory system, the lymphatic system drains excess tissue fluid and plays a role in immune function.

Summary

The circulatory system maintains homeostasis by transporting essential substances and protecting the body from pathogens through its integral components: blood, the heart, blood vessels, and the lymphatic system.### Blood Types and Rh Factor
Blood type B can receive donations from type B and O.
Rh system categorizes blood based on D antigen presence: Rh+ (presence) and Rh- (absence).
"Rh" stands for Rhesus, the monkey where the antigen was first discovered.
Rh compatibility is crucial; Rh+ blood should not be given to Rh- recipients due to potential sensitization.
Sensitization occurs when Rh- individuals develop antibodies to Rh+ blood, leading to severe reactions in future transfusions.
Rh- mothers carrying Rh+ babies may face complications in subsequent pregnancies, necessitating Rh factor screening.

Blood Vessels

Blood vessels are tubular structures that transport blood throughout the body, classified into arteries, veins, and capillaries.

Arteries

Carry blood away from the heart; characterized by thick muscular walls, narrow lumen, and elasticity.
Do not contain valves and are generally located deeper in the body.
Except for the pulmonary artery, arteries carry oxygenated blood and can constrict or dilate to regulate flow.
Smallest branches of arteries are arterioles, which lead to capillaries.

Veins

Transport blood towards the heart; possess thin muscular walls and wider lumen compared to arteries.
Have pocket-shaped valves that prevent backflow.
Generally carry deoxygenated blood (except for pulmonary veins) and are located nearer to the skin surface.
Collapse when empty and progressively unite to form larger veins.

Capillaries

Microscopic blood vessels with single-layer squamous epithelial walls.
Lack muscular structure and facilitate diffusion of oxygen, carbon dioxide, nutrients, and waste products.
Regulate blood flow via vasodilation and vasoconstriction, affecting skin color in response to temperature changes.

Circulatory System Overview

Comprises the heart and blood vessels, responsible for circulating blood throughout the body.

Heart Location and Structure

Positioned above the diaphragm, between the lungs, with a triangular shape approximately the size of a closed fist.
Covered by a pericardium consisting of two walls and lubricating pericardial fluid to reduce friction.
Divided into four chambers: two atria (upper) and two ventricles (lower), each responsible for different functions.

Heart Valves

Right atrio-ventricular valve (tricuspid) between right atrium and ventricle has three flaps.
Left atrio-ventricular valve (bicuspid or mitral) between left atrium and ventricle has two flaps.
Pulmonary and aortic semilunar valves at the openings of the right and left ventricles respectively.

Blood Circulation

Blood enters the right auricle via venae cavae and the left auricle via pulmonary veins.
Atrial contraction pushes blood into ventricles, followed by ventricular contraction that sends blood into pulmonary artery and aorta.
The heart operates in a cycle of systole (contraction) and diastole (relaxation) involving all four chambers.

Heartbeat and Blood Pressure

One heartbeat involves a complete cycle of contraction and relaxation lasting approximately 0.85 seconds.
Normal ranges: systolic pressure (100-140 mm Hg), diastolic pressure (60-80 mm Hg).
Hypertension defined as blood pressure above 140/90 mm Hg.

Pacemaker and Heart Rate

Sino-atrial node (SAN) generates electrical impulses to trigger heart contractions; acts as the natural pacemaker.
Atrioventricular node (AVN) and the Bundle of His assist in regulating heart rate. Placement of artificial pacemakers may be needed if issues arise.

Circulation Types

Pulmonary Circulation: Blood flows between the heart and lungs for oxygenation.
Systemic Circulation: Oxygenated blood delivered from the heart to the body, returning deoxygenated blood via veins.

Hepatic Portal System

A portal system connects capillaries of the digestive tract to the liver via the hepatic portal vein, facilitating nutrient transport and detoxification.

Lymphatic System

Works in parallel with the circulatory system, involved in transporting tissue fluid and lymph.
Lymph is collected from intercellular spaces and transported through lymph vessels to the bloodstream.
Functions include nutrient transport, fat absorption via lacteals, and immune defense through lymphocytes.### Lymphatic System and Spleen
The spleen is a lymphatic organ that contains lymphoid tissues, playing a crucial role in immune function.
Located behind the stomach and above the left kidney, it has a reddish-brown color.
During embryonic development, the spleen is responsible for the production of red blood cells (RBCs).
In adults, the spleen produces lymphocytes and is involved in the destruction of old and worn-out RBCs.
It functions as a blood reservoir, storing blood that can be released during hemorrhage, physical or emotional stress, or carbon monoxide poisoning.

Circulatory System

Blood serves as the primary circulating fluid in the body, comprising formed elements: red blood cells (erythrocytes), white blood cells (leucocytes), and platelets (thrombocytes).
Hemoglobin within RBCs binds with oxygen to form oxyhemoglobin, which is released readily in tissues needing oxygen.
The phagocytosis process allows WBCs to engulf foreign substances and microbes as part of the immune response.
Blood clotting is the coagulation process that occurs at injury sites, preventing excessive blood loss.
RBCs have surface proteins called antigens, determining blood types.
Blood groups are classified into A, B, AB, and O types based on antigen presence.
Type O blood is known as the universal donor, while type AB blood is considered the universal recipient.
The Rh system classifies blood based on the presence of D antigen.

Heart and Blood Vessels

Blood vessels are categorized into three types: arteries, veins, and capillaries.
Veins carry blood towards the heart, transporting deoxygenated blood from organs to the heart.
Capillaries facilitate the exchange of oxygen and carbon dioxide between blood and interstitial fluid.
The heart has four chambers: two atria (upper chambers) and two ventricles (lower chambers).
A cardiac cycle consists of one heartbeat, marked by a contraction phase (systole) and a relaxation phase (diastole).
Each heartbeat lasts approximately 0.85 seconds, and pulse is the alternate expansion and contraction of arterial walls.
Heart rate varies with the organism's size; smaller bodies generally have faster heart rates.
Blood exerts pressure on arterial walls known as blood pressure, with normal systolic pressure ranging from 100-140 mmHg and diastolic pressure from 60-80 mmHg.
The sino-atrial node (SAN) functions as the heart's pacemaker, regulating heart rate.

Hepatic Portal System and Lymphatic System

A portal system begins and ends with capillaries; the hepatic portal system is a primary example in the body.
Tissue fluid, or intercellular fluid, leaks from capillaries into the spaces between cells.
The lymphatic system plays a vital role in defense against pathogens.
The spleen functions as a critical component of the lymphatic system, supporting both immune function and blood regulation.