Lecture 14: Blood Vessels and Hemodynamics PDF

Lecture 14: Blood vessels and hemodynamics ========================================== **Please read pages 771--838 (excluding 21.23) for this lecture.** **Learning Objectives:** - Compare and contrast the structures and functions of: arteries, arterioles, capillaries, venules, and veins. -...

Lecture 14: Blood vessels and hemodynamics ========================================== **Please read pages 771--838 (excluding 21.23) for this lecture.** **Learning Objectives:** - Compare and contrast the structures and functions of: arteries, arterioles, capillaries, venules, and veins. - Trace the passage of blood after its exit from the heart ventricles through the body and back to the heart. - Explain the difference between a blood pressure reservoir and a blood reservoir. - Define blood reservoirs and their importance to the cardiovascular system. - Explain the physical principles behind the movement of fluid between blood and interstitial fluid at capillary networks, especially: diffusion, transcytosis, and bulk flow. - Identify the factors that regulate blood flow and explain how they exert their effects. - Explain how blood pressure changes at different locations in the cardiovascular system. - Define resistance as it pertains to blood velocity and explain how resistance is modulated within the cardiovascular system. - Explain how the total cross-sectional area of blood vessels and the velocity of blood flow is correlated. - Explain the factors that regulate blood pressure and why maintaining a specific blood pressure is critical to homeostasis. - Define shock and identify potential causes and treatments of shock. - Define hypertension and explain how hypertension can be prevented and treated. Blood vessel structure and function ----------------------------------- ### Introduction - There are five main types of blood vessels: 1. Arteries 2. \_\_\_arterioles\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ 3. Capillaries 4. Venules 5. Veins - All form one large interconnected \_\_\_loop\_\_\_\_\_\_ - Arteries and arterioles - Carry blood away from the heart - Large **\_\_\_elastic\_\_\_\_\_\_\_** arteries carry blood from heart - Branch into **\_\_\_\_\_muscular\_\_\_\_\_\_\_\_** medium-sized arteries - Small arteries branch into **arterioles** A picture containing text Description automatically generated  **Above left**: Blood vessels form one large interconnected loop. **Above right:** Structure of blood vessels. - Capillaries facilitate exchange between blood and tissues - Arterioles branch into tissues and become **blood** **capillaries** - Very small in diameter - Thin walls facilitate \_\_\_\_\_\_exchange\_\_\_\_\_\_\_\_\_ between tissues and blood - Veins and venules - Capillaries merge into small veins called **\_\_\_\_\_\_venules\_\_\_\_\_\_\_\_** - Venules merge into larger vessels called **veins** - Veins \_\_\_\_\_return\_\_\_\_\_\_ blood to the heart ### Blood vessel structure - Layers of blood vessels are called **\_\_\_\_tunics\_\_\_\_** - **Tunica interna**: endothelial lining in direct contact with blood - **Tunica media**: intermediate layer of \_\_\_\_\_\_smooth\_\_\_\_\_\_ muscle + CT - **Tunica externa**: surrounding CT layer - The tunica interna lines blood vessel walls - Thin endothelial lining in direct contact with blood - Facilitates exchange by \_\_\_\_\_\_diffusion\_\_\_\_\_\_\_ - Provides a smooth surface for blood to flow over - Recall: endothelium \_\_\_\_\_\_secretes\_\_\_\_\_\_\_ **NO** and other vascular regulators Diagram Description automatically generated - **Basement membrane** surrounds endothelium - \_\_\_\_\_\_\_anchors\_\_\_\_\_\_\_ endothelium to underlying tissues - Provides \_\_\_\_\_tensile\_\_\_\_\_\_\_ strength to lining - Acts as a substratum for cell migration during wound healing - Superficial to basement membrane = thin sheet of **elastic fibres** - Maintains \_\_\_\_\_\_\_extensibility\_\_\_\_\_\_\_\_\_\_\_ of blood vessels - Tunica interna contains large \_\_\_\_pores\_\_\_\_\_\_ - Large molecules can simply diffuse into/out of blood - The tunica media - Varies between vessel type - Thick layer of smooth muscle and elastic fibres - Mediates **\_\_\_\_\_\_\_\_\_vasocontraction\_\_\_\_\_\_\_\_\_\_\_\_** = decrease in lumen diameter - And **\_\_\_\_\_\_\_\_\_\_vasodilation\_\_\_\_\_\_\_\_\_** = increase in lumen diameter -... in response to many signals - During vasoconstriction, smooth muscle fibres **contract** - During vasodilation, smooth muscle fibres **relax** - Superficial to the smooth muscle is another sheet of elastic fibres - Confers extensibility and \_\_\_\_\_\_\_elasticity\_\_\_\_\_\_\_\_\_ to blood vessels - The tunica externa - Made mostly of \_\_\_\_\_\_\_collagen\_\_\_\_\_\_\_\_\_ and elastic fibres - Contains many nerves - Large blood vessels serviced by many tiny vessels - Called the **vasa vasorum** - Example: outside the \_\_\_\_\_\_aorta\_\_\_\_\_ - Summary of blood vessel structure: - Large elastic arteries carry blood from the heart; branch into muscular arteries - Muscular arteries branch into arterioles become capillaries at tissues - Capillaries merge into venules as they exit tissues merge into veins - Veins carry blood back to the heart - Arteries and veins have all three tunics - Capillaries possess the tunica interna + basement membrane ### Organization of the circulatory system #### Elastic arteries - Enriched with elastic fibres + thin wall of smooth muscle - Push blood from the heart during **ventricular diastole** - Blood stretches the elastic fibres in the tunica interna and media, creating a **pressure \_\_\_\_\_\_reservoir\_\_\_\_\_\_\_\_\_** - ***What is this?*** **When you have ventricular systole, it creates a large pressure and the aorta is elasticity and can handle the immense pressure** - A.k.a. **conducting arteries** because they rout blood from the heart  #### Muscular arteries - \_\_\_\_\_\_thicker\_\_\_\_\_\_ layer of smooth muscle than elastic arteries - Very \_\_\_\_\_\_loose\_\_\_\_\_\_ tunica externa permits stretching during vasoconstriction or vasodilation - Also known as **distributing arteries** because they move blood into multiple small arterioles - Anastomoses are places that vessels of related function join one another - **\_\_\_\_\_\_\_\_\_\_\_anastomosis\_\_\_\_\_\_\_\_\_\_\_:** point that multiple blood vessels servicing the same body region join each other - Provides bypasses for blood during **\_\_\_\_\_\_collateral\_\_\_\_\_\_\_\_\_ circulation** - Movement compresses an artery and restricts blood flow - Occurs between arteries, veins, arterioles, and venules Diagram Description automatically generated - Arteries without anastomoses are called **\_\_\_\_end\_\_\_ arteries** - Block to circulation through end arteries can lead to tissue death or **\_\_\_\_\_\_\_necrosis\_\_\_\_\_\_\_\_\_**  **Circle or box** the name of an *end artery* on the diagram above. #### Arterioles - **Arterioles** are microscopic arteries - Diameter varies widely (15--300 μm) - Vessel wall thickness = \_\_50\_\_\_% of vessel diameter - \_\_\_\_\_\_regulate\_\_\_\_\_\_\_\_\_ flow of blood into capillaries - Porous elastic lamina in tunica interna - Tunica media = 1-2 layers of ring-shaped smooth muscle - Narrows at entry into capillary beds - Narrowed sections called **\_\_\_\_\_\_\_\_metarterioles\_\_\_\_\_\_\_\_** - Distal muscle of metarteriole forms **precapillary \_\_\_\_\_\_\_sphincter\_\_\_\_\_\_\_\_\_** - \_\_\_\_nerves\_\_\_\_\_\_\_ in tunica externa of metarterioles - \_\_\_\_\_regulate\_\_\_\_\_\_\_\_\_\_ vessel diameter - Critical to arteriole function Diagram Description automatically generated - How do arterioles work? - Arterioles modulate **\_\_\_\_\_\_\_\_\_\_resistance\_\_\_\_\_\_\_** - Friction blood experiences as it flows over blood vessel walls - **Vasoconstriction** *\_\_\_\_\_\_increases\_\_\_\_\_\_\_\_\_* blood contact with walls - Increased friction - Increased resistance #### Capillaries - Smallest of the blood vessels (5--10 μm diameter) - Extensively \_\_\_\_\_\_branching\_\_\_\_\_\_\_\_ networks ensure all body cells have access to nutrients, signals, and a way to eliminate wastes - Organs with high \_\_\_\_\_\_\_\_metabolic\_\_\_\_\_\_\_\_\_\_ activities have higher capillary density (e.g. brain \> tendons) - Primary function = **exchange with interstitial fluid** - *Question*: The diameter of an erythrocyte = 8 μm.  **Above left**: Capillaries are thin blood vessels that permit single file passage of erythrocytes. **Above right**: Erythrocytes squeeze between endothelial cells when they leave blood. - Capillaries have a unique structure - Lack both tunica externa and tunica media - Only endothelium + basement membrane - Diffusion occurs across single cell layer - Capillary beds = many branches that increase \_\_\_\_\_\_surface\_\_\_\_\_\_ \_\_\_\_area\_\_\_\_ Diagram Description automatically generated - What is a **capillary bed**? - Branching from metarterioles into 10-100 capillaries. - Two routes for blood from metarterioles to venules: 1. **Through capillaries** - Blood enters capillary beds - Exits via \_\_\_\_\_\_\_\_\_\_\_postcapillary\_\_\_\_\_\_\_\_\_\_ venules - Called **\_\_\_\_\_\_\_\_\_microcirculation (blood going into capillary bed)\_\_\_\_\_\_\_\_\_\_\_\_** - Rate of precapillary sphincter contraction - 5--10 times per minute - Called **\_\_\_\_\_\_\_\_\_vasomotion\_\_\_\_\_\_\_\_\_\_\_** - Regulated by hormones (e.g. NO) - Only \_\_\_\_25\_\_\_\_% of blood flowing through capillaries at a given time 2. **Through a \_\_\_\_\_\_\_\_\_\_throughfare\_\_\_\_\_\_\_\_\_\_\_\_\_ channel** - No smooth muscle proximal to metarteriole end - Permits direct flow through precapillary sphincters to \_\_\_\_\_\_\_venules\_\_\_\_\_\_\_  - There are three types of capillaries 1. **\_\_\_\_\_\_\_\_continuous\_\_\_\_\_\_\_\_\_ capillaries** - Smooth, continuous endothelium - Interrupted only by **intercellular \_\_\_\_\_cleft\_\_\_\_\_\_\_** between adjacent endothelial cells - Found in the organs of CNS, lungs, muscle, and skin 2. **\_\_\_\_\_\_\_\_\_\_fenestrated\_\_\_\_\_\_\_\_ capillaries** - Endothelial cells have "windows" or \_\_\_\_pores\_\_\_\_\_ called **fenestrations** - **Permit diffusion of proteins and other molecules** - Found in kidneys, small intestinal villi, eyes, and endocrine glands. 3. **\_\_\_\_\_\_sinusoids\_\_\_\_\_\_\_\_\_\_\_** - Wider and "twistier" than other types - Little to no basement membrane - Large fenestrations and intercellular clefts - Reticulocytes enter circulation from red bone marrow through sinusoids - Lining may have specialized function in some organs - Found in the \_\_\_\_\_liver\_\_\_\_\_\_, spleen, anterior pituitary, parathyroid, and adrenal glands. #### Venules and veins - Thin walls lose shape easily - Cannot withstand same \_\_\_\_\_\_\_pressure\_\_\_\_\_\_\_\_\_ as arteries/arterioles - **Muscular venules** are **\_\_\_\_\_\_\_distensible\_\_\_\_\_\_\_\_** and can withstand some pressure - Accumulate large blood volumes - Largest recorded = 360% volume! Diagram Description automatically generated  **Above left**: Structures of the three types of capillaries. **Above right:** Comparison between artery and vein structure. - Veins change shape as they merge into larger vessels but all are thin-walled - Walls are 10% of vessel diameter - Diameter ranges from 0.5 μm to 3 cm - Contain \_\_\_\_\_valves\_\_\_\_\_ to prevent backflow of blood - Thick tunica externa - Contributes to distensibility - Large lumens; appear collapsed in microscopic section - Systemic veins and venules act as blood reservoirs - **Blood reservoirs** are places in the body that store large volumes of blood - Blood can be redirected from these based on need - What are the **principal blood reservoirs?** - Where is the smallest proportion of our blood volume found? Diagram Description automatically generated  **Above left**: Structure of the valves of veins. **Above right**: Distribution of blood throughout the body. Capillary exchange ------------------ - Capillary exchange is an essential function of the cardiovascular system - The heart pumps blood so that the blood can exchange materials with the \_\_\_\_\_tissues\_\_\_\_\_ through capillaries - **Capillary exchange**: movement of substances between blood and \_\_\_\_\_\_interstitial\_\_\_\_\_\_\_\_\_\_ \_\_\_fluid\_\_\_\_\_ - Three mechanisms of capillary exchange: 1. **\_\_\_\_\_\_diffusion\_\_\_\_\_\_\_\_\_** - Through fenestrations, intercellular clefts, or endothelial cell membranes - E.g. Gases, solutes, amino acids, glucose and other hormones - Sinusoids permit passage of proteins like \_\_\_\_\_\_\_fibrinogen\_\_\_\_\_\_\_\_ - Most capillaries in the brain are continuous capillaries with tight intercellular junctions - Result: high selective permeability of **blood-brain barrier** 2. **\_\_\_\_\_\_\_\_\_\_transcytosis\_\_\_\_\_\_\_\_\_\_\_\_\_** - Relatively rare method of exchange - Recall: **pinocytosis** = bulk uptake of materials by cells - Pinocytic vesicles containing large molecules cross this way - E.g. Insulin entering the bloodstream or maternal \_\_\_\_\_\_\_antibodies\_\_\_\_\_\_\_\_\_ crossing the placenta into fetal blood Diagram Description automatically generated 3. \_\_\_\_\_\_bulk\_\_\_\_\_ \_\_\_\_\_flow\_\_\_\_\_ - The **collective** movement of large volumes of molecules from an area of **high pressure to low pressure** - Regulates the relative volumes of blood and interstitial fluid - Bulk flow is regulated by fluid pressures - Movement from blood into interstitial fluid is called **\_\_\_\_\_\_filtration\_\_\_\_\_\_\_** - Movement from interstitial fluid into blood is called **\_\_\_\_\_\_\_\_\_\_reabsorption\_\_\_\_\_\_\_\_\_\_**  - **Net filtration pressure** is the difference between filtration and reabsorption - Bulk flow is driven by **net filtration pressure (NFP)** - Determines whether \_\_\_\_\_\_relative\_\_\_\_\_\_ blood and interstitial fluid volumes change - OVERALL: volume reabsorbed \~ volume filtered - *Why is this so important?* - NFP consists of hydrostatic and osmotic pressures - Think of a hydrostatic pressure as a **\_\_\_push\_\_\_\_** - **Blood hydrostatic pressure (BHP)** - Pressure of water in blood plasma *pushing* on endothelium - Caused by forceful ejection of blood from the ventricles - Higher at **arterial end** than **venous end** of capillaries - Contributes to **\_\_\_\_\_\_\_\_filtration\_\_\_\_\_\_\_\_\_\_\_\_\_** - **Interstitial fluid hydrostatic pressure (IFHP)** - Pressure of water from interstitial fluid *pushing* on basement membrane of capillaries - Very weak -- no "pump" - \_\_\_\_\_\_\_\_constant\_\_\_\_\_\_\_\_ pressure along length of capillaries - Contributes to \_\_\_\_\_\_\_\_reabsorption\_\_\_\_\_\_\_\_\_\_\_\_\_\_ - Think of osmotic pressures as a \_\_\_\_Pull\_\_\_\_\_ - **Blood colloid osmotic pressure (BCOP)** - Pressure exerted by solutes and proteins in blood (colloid) that *pulls* on water in interstitial fluid (osmotic) - Blood is relatively **\_\_\_\_\_\_hypertonic\_\_\_\_\_\_\_\_\_\_\_\_** as compared to interstitial fluid - Maintained by continuous generation of blood proteins (e.g. fibrinogen) - Should be constant within blood - **Interstitial fluid osmotic pressure (IFOP)** - Pressure exerted by solutes in interstitial fluid that *pulls* on water in blood plasma - Some solutes are kept at constantly higher concentration in interstitial fluid than blood - Very weak pressure = 1 mmHg (\_\_\_\_\_\_\_\_negligible\_\_\_\_\_\_\_\_\_) - What happens to filtered fluid? - 85% of fluid filtered from capillaries is \_\_\_\_\_\_reabsorbed\_\_\_\_\_\_\_\_\_ - Remaining 15% is taken up by \_\_\_\_lymph\_\_\_\_\_\_ vessels - Returned to circulation at subclavian veins - What happens if filtered fluid accumulates? - **Edema** is an increase in interstitial fluid volume - **Lymph edema** results from a failure of lymphatic vessels to filter properly - More in Biol 2292 (Patho II) - May also be caused by **protein deficiency** - *How does this work?* A picture containing person, clothing, floor, indoor Description automatically generated - Summary of capillary exchange: - Substances can move between interstitial fluid and blood in three ways: - Diffusion - Transcytosis - Bulk flow - Bulk flow is the mass movement of substances according to **pressure gradients** - NFP = (BHP + IFOP) -- (BCOP + IFHP) or **net filtration - net reabsorption** Hemodynamics ------------ - Hemodynamics is the study of the forces that affect blood flow in the body - **Blood flow** is the volume of blood flowing through a given tissue at a particular time (mL/min.) - Total blood flow = cardiac output (CO) - Extent of blood flow to a particular area is known as **perfusion** - Two things modulate blood flow: 1. **Blood pressure** 2. **Vascular resistance** - What is blood pressure? - **Blood pressure (BP)** is the \_\_\_\_\_\_\_hydrostatic\_\_\_\_\_\_\_\_\_ pressure that blood exerts on blood vessel walls - Generated by contraction of the ventricles - Highest in the aorta - **Systolic blood pressure** is the highest BP in arteries during cardiac systole - **Diastolic blood pressure** is the lowest BP in arteries during cardiac diastole - **Blood flows from high to low pressures**  - - - - - - Factors affecting blood pressure - Small changes to blood volume almost no effect on BP - Any changes 10% or greater in total blood volume will change BP - E.g. You had a fun night out but it's the morning after and you are **retaining water** like a kitchen sponge. *What is this excess fluid doing to your **blood pressure**?* - Vascular resistance opposes blood flow - Recall: resistance = forces of \_\_\_\_\_\_friction\_\_\_\_\_\_ that oppose blood flow through a vessel - Vascular resistance (VR) is resistance in the circulatory system - VR is affected by: 1. **\_\_\_\_\_\_diameter\_\_\_\_\_\_\_\_\_ of vessel lumen** - Recall: vasoconstriction increased resistance - Constriction of arterioles increased VR increased BP overall - Decreases blood flow 2. **Blood viscosity** - Thickened blood = increased VR increased BP - E.g. Polycythemia or blood doping 3. **Total vessel length** - Longer vessels = greater \_\_\_\_\_\_surface\_\_\_\_\_\_ \_\_area\_\_\_\_ in contact with blood increased resistance and BP - Venous return: movement of blood from capillaries to the heart - Recall: blood moves according to pressure differentials - Pressure at entry to right atrium = 0 mmHg - How could the body increase the rate of **venous return**? - Could pump blood more forcefully from heart - If BP increased within the right atrium **\_\_\_\_\_\_\_\_decreases\_\_\_\_\_\_\_\_** the rate of **venous return** - Two pumps move blood back to the heart: 1. **Skeletal muscle pump** - \_\_\_\_\_\_\_movement\_\_\_\_\_\_\_\_\_ of skeletal muscle \_\_\_\_\_\_\_\_\_compresses\_\_\_\_\_ veins - Produces pressure gradients - **Valves** prevent backflow Diagram Description automatically generated - How does the skeletal muscle pump work? - At rest, venous valves are **\_\_\_open\_\_\_\_\_** - When you move, contraction of skeletal muscle compresses veins - Pushes blood through proximal valve - **\_\_\_\_\_closes\_\_\_\_\_\_** distal valve - New movement generates enough pressure to re-open distal valve - Movement starts cycle again 2. The respiratory pump - Recall: the diaphragm separates the thoracic and abdominopelvic cavities - During inhalation, diaphragm contracts and **\_\_\_\_\_increases\_\_\_\_\_\_\_\_** thoracic cavity volume - Simultaneously **\_\_\_\_\_\_\_\_\_compresses\_\_\_\_\_\_\_** the abdominal cavity - Blood in compressed abdominal veins moves to decompressed thoracic veins - During exhalation, venous valves prevent backflow of blood - Try answering this commonly asked question on your own: How does blood return to the heart when we sleep?! - Summary  - What is blood velocity? - The **\_\_\_\_speed\_\_\_\_\_** (distance/time) at which blood flows - Inversely proportional to **total \_\_\_cross\_\_\_-\_\_\_\_\_\_sectional\_\_\_\_\_\_ diameter** - Vascular resistance strongly influences blood velocity Diagram Description automatically generated - The cardiovascular centre regulates heart and vascular function - Recall: HR is the primary means by which the body will change CO and, therefore, **blood pressure** - The cardiovascular centre can signal for **increased** or **decreased:** - Heart rate (HR) - Heart \_\_\_\_\_\_contractibility\_\_\_\_\_\_\_ - Can also act directly on blood vessels, stimulating **vasoconstriction or** **vasodilation**  - Hormones regulate blood pressure and blood flow - There are many hormones that affect blood pressure and blood flow, including: 1. **The renin-angiotensin-aldosterone system (RAA)** - \_\_\_\_\_\_\_\_decreases\_\_\_\_\_\_\_\_ blood pressure to the kidneys triggers hormone production that decreases \_\_\_\_\_urinary\_\_\_\_ output - Increased blood volume increases blood pressure 2. **Epinephrine/norepinephrine** - Affects release of \_\_\_\_\_calcium\_\_\_\_\_\_\_\_ into cytosol of cells, including cardiac muscle cells and smooth muscle around blood vessels 3. **Anti-diuretic hormone (ADH)** - A.k.a**.** **vasopressin** is made in the **hypothalamus** - Secreted from the **pituitary gland** in response to dehydration/low blood volume - Stimulates **\_\_\_\_\_\_\_\_\_\_vasocontriction\_\_\_\_\_\_\_\_\_\_\_\_** to increase blood pressure 4. **Atrial \_\_\_\_\_\_\_natriuretic\_\_\_\_\_\_\_\_ peptide (ANP)** - Released by cardiac atrial cells to stimulate vasodilation - Reduces salt and water reabsorption in the kidneys - Net effect: decreased blood volume and \_\_\_\_\_\_decreased\_\_\_\_\_\_\_\_\_ BP - Summary of hormonal control Graphical user interface, text, application Description automatically generated - **\_\_\_\_\_\_\_\_\_autoregulation\_\_\_\_\_\_\_\_\_** of flow means blood vessels can change their own physiology to meet metabolic demand - Two main inputs: 1. **Physical changes** - Temperature of a tissue or \_\_\_\_\_\_\_\_stretching\_\_\_\_\_\_ of an elastic artery/vein - Increased metabolic activity of an organ leads increased blood flow to that organ 2. **Vasodilators/vasoconstrictors** - Substances that increase/decrease blood vessel diameter - Includes NO, K^+^, Na^+^, superoxide, etc. - **\_\_\_\_\_\_\_\_systemic\_\_\_\_\_\_\_\_ blood vessels** dilate in response to low oxygen - Increases tissue perfusion - **Pulmonary blood vessels** constrict in response to low oxygen - Ensures that only \_\_\_\_\_\_\_\_undamaged\_\_\_\_\_\_\_ alveoli are used to oxygenate blood ### Homeostatic imbalances of the vascular system - **Shock**: insufficient delivery of \_\_\_\_\_oxygen\_\_\_\_\_\_ and nutrients to meet the body's metabolic needs - Many different kinds of shock: - **Hypovolemic shock**: caused by excessive \_\_\_\_\_\_\_dehydration\_\_\_\_\_\_\_\_ (e.g. sweating, vomiting) decreased blood volume - **Cardiogenic shock**: damage to the heart (e.g. infarction, valve defects) inability to pump blood - **Anaphylactic shock**: excessive production of \_\_\_\_\_\_\_histamine\_\_\_\_\_\_\_ and vasodilators decreased BP - **Neurogenic shock**: head trauma inability to sense and respond to changes in BP - **Septic shock**: bacterial toxins cause excessive vasodilation - **Obstructive shock**: block to circulation (e.g. \_\_\_\_\_\_\_\_\_embolism\_\_\_\_\_\_\_\_)  A picture containing table Description automatically generated **Above left**: Consequences of anaphylactic shock include swelling, production of a red rash, and constriction of airways. **Above right**: Classification of hypertension by blood pressure ranges. - Physiological responses to shock - To restore the delivery of oxygen and nutrients, the body may: 1. **Stimulate** **the RAA pathway** to increase blood volume 2. **Release ADH** to increase blood volume 3. **Stimulate \_\_\_\_\_\_\_\_sympathetic\_\_\_\_\_\_\_\_\_ nervous responses** - Leads to both **vasoconstriction** and **venoconstriction** 4. **Release \_\_\_\_local\_\_\_\_\_ vasodilators** to increase blood flow to specific tissues - What is **hypertension**? - Persistently elevated blood pressure - Increases risk of heart failure, kidney disease, and stroke - 90-95% of cases are **\_\_\_\_\_\_\_idiopathic\_\_\_\_\_\_\_\_** - No identifiable cause - 5-10% of cases can be traced to a physiological cause Circulatory routes ------------------ - There are two main circulatory routes: 1. **Systemic circulation** - Includes: coronary, \_\_\_\_\_\_\_cerebral\_\_\_\_\_\_\_, and hepatic portal circulation 2. **Pulmonary circulation** ### Systemic circulation - The function of systemic circulation: - Is to distribute \_\_\_\_\_\_oxygenated\_\_\_\_\_\_\_\_\_\_\_ blood from the left ventricle to all of the body's tissues - Also returns deoxygenated blood to the right atrium  Diagram Description automatically generated **Above left**: Schematic of the two main circulatory routes in the human body. **Above right**: The systemic arteries. #### Cerebral circulation - The cerebral arterial circle - Four major arteries service the head - *Can you name them?* - A **number** of **anastomoses** that ensure that your brain will be \_\_\_\_\_\_\_perfused\_\_\_\_\_ \_\_\_\_\_\_\_\_constantly\_\_\_\_\_\_\_\_ - Formerly the circle of Willis - **Internal \_\_\_\_\_carotid\_\_\_\_\_\_ artery** branches into: - The **anterior cerebral artery** (services the frontal lobe) - The **middle cerebral artery** (runs between temporal and parietal lobes) -... on the left and right sides - The left and right anterior cerebral arteries are joined by the **anterior \_\_\_\_\_\_\_\_\_communicating\_\_\_\_\_\_\_\_\_\_\_ artery** - Similarly, the left and right **posterior cerebral arteries** are anastomosed via the **posterior communicating artery** - Collectively forms the **\_\_\_\_carotid\_\_\_\_\_\_\_\_-\_\_\_\_\_basilar\_\_\_\_\_ artery anastomosis** Diagram Description automatically generated **Above left**: Schematic of systemic arteries servicing the head and brain. **Above right**: The cerebral arterial circle. ­­­­  **Above:** Systemic veins. #### Hepatic portal circulation - A **\_\_\_\_\_portal\_\_\_\_\_\_ vein** carries blood between two capillary networks - **Hepatic portal circulation** carries blood from the gastrointestinal organs and spleen to the liver - Hepatic capillaries are mostly **sinusoids** - Nutrient-rich blood can pass large molecules to liver cells for **\_\_\_\_\_\_anabolism\_\_\_\_\_\_\_\_, storage, or detoxification** Diagram Description automatically generated - The **hepatic portal vein** carries nutrient-rich but deoxygenated blood - *What **artery** brings oxygenated blood to the liver?* *Hepatic artery* - The **hepatic veins** return deoxygenated, nutrient-poor blood to the right atrium via the inferior vena cava ### Pulmonary circulation - Brings deoxygenated blood from the right ventricle to the alveoli of the lungs for **\_\_\_\_\_\_\_\_\_oxygenation\_\_\_\_\_\_\_\_\_\_\_** - Also routs oxygenated blood to left atrium - DOES NOT provide oxygen to lung tissues! Diagram Description automatically generated ### Fetal circulation - Occurs only in the fetus - Lungs, kidneys, and gastrointestinal organs do not function until *after* birth - Exchange of substances between mother and fetus occurs through the **\_\_\_\_\_placenta\_\_\_\_\_** - Both maternal and fetal tissues form part of the placenta - Maternal and fetal blood **NEVER** mixes - Fetal portion of the placenta joins fetal circulation through the **\_\_\_\_\_umbilical\_\_\_\_\_\_\_ cord** - Oxygenated, nutrient-rich maternal blood diffuses into fetal capillaries - Carried to the fetus via the **umbilical \_\_vein\_\_\_\_\_** - Blood splits at fetal liver: - Hepatic portal vein - **\_\_\_\_\_\_ductus\_\_\_\_\_\_ \_\_\_\_\_\_\_\_\_venosus\_\_\_\_\_\_\_** - Ductus venosus drains into the inferior vena cava - Drains into the right atrium - Blood travels from the right atrium **directly into the left atrium** through the **\_\_\_\_\_foramen\_\_\_\_\_\_\_\_ \_\_\_\_\_\_ovale\_\_\_\_\_\_\_** - Remember: fetal lungs are not functional! - Small amount of blood entering pulmonary trunk travels into **aorta** through the **\_\_\_\_\_\_ductus\_\_\_\_\_\_\_\_ \_\_\_\_\_\_\_arteriosus\_\_\_\_\_\_\_\_\_\_\_** - Mix of oxygenated and deoxygenated blood pumped through systemic circulation - Deoxygenated blood containing metabolic wastes drains from the **\_\_\_\_\_internal\_\_\_\_\_\_\_ \_\_\_\_\_\_iliac\_\_\_ arteries** into the **umbilical \_\_\_\_\_\_\_artery\_\_\_\_\_\_** - Back to placenta diffuses into maternal blood at **uterine arteries**  Summary ------- - Systemic circulation distributes oxygenated blood to all of the body's tissues and returns deoxygenated blood to the right atrium - Includes hepatic portal circulation - The cerebral arterial circle is critical to maintain constant perfusion of the brain - Pulmonary circulation oxygenates blood and returns it to the left atrium - Fetal circulation is unique to the fetus and includes unique structures - The ductus venosus permits oxygenated blood to drain into the inferior vena cava - The ductus arteriosus permits blood in the pulmonary trunk to bypass the lungs aorta - The umbilical artery carries blood away from the fetus; the umbilical vein carries oxygenated blood to the fetus