Circulation and Short-Term Blood Pressure Regulation

Circulation and Short-Term Blood Pressure Regulation

Page 1 - Introduction

This note explains how blood moves around the body (circulation) and how blood pressure is controlled.

Page 2: Profiles in A&P: William Harvey

  • William Harvey (1578 to 1657): A British Doctor

    • Studied in England and Italy, earning his doctorate at the University of Padua before returning to England.

    • Worked as a doctor and college lecturer, and was involved with King Philip.

    • Testified at the trial of George Villier (who was acting king) when Philip died from poisoning; Villier was later found not guilty.

    • Was involved in witch trials, trying to find scientific reasons to clear people.

    • What he did: He was the first to explain how blood circulates in the body, showing it makes a full loop starting and ending in the heart.

    • What people thought before: They used to believe there were separate blood systems and that the body just used up the blood.

Page 3: Structure and Function of Blood Vessels

Looks at the different kinds of tubes (blood vessels) that carry blood and what they do.

Page 4: Principles of Hemodynamics

  • Blood Flow (F): How much blood moves through a tube, body part, organ, or the whole body in a certain amount of time.

  • Blood Pressure (BP or P): The pushing force of blood against the wall of a blood vessel, measured in mmHgmm Hg.

  • Resistance (R): The friction that slows down blood flow.

  • Three things affect resistance:

    1. How thick the blood is (blood viscosity)

    2. How long the blood vessel is

    3. How wide the blood vessel is (blood vessel radius)

Page 5: Blood Pressure and Flow

  • Arterial Blood Pressure (BP): This is usually what people mean when they talk about "blood pressure."

  • Systolic Pressure (SP): The pressure in vessels when your heart's pumping chambers (ventricles) squeeze.

  • Diastolic Pressure (DP): The pressure in vessels when your heart's pumping chambers (ventricles) relax.

  • Mean Arterial Pressure (MAP): The average pressure in your arteries over one full heartbeat cycle. It's affected by how much blood your heart pumps and how much resistance there is.

    • Formula: MAP=DP+13(SP−DP)MAP = DP + \frac{1}{3}(SP - DP)

  • Pulse Pressure (PP): The difference between your systolic and diastolic pressures.

    • Formula: PP=SP−DPPP = SP - DP

Page 6: Basic Structure of Blood Vessels

  • Tunica Intima: The inner smooth lining of blood vessels, which is continuous throughout the whole blood system.

  • Elastic Lamina: Stretchy layers found only in arteries, both inside and outside the middle layer.

  • Tunica Media: The middle layer, containing smooth muscle, which helps blood vessels to narrow (vasoconstriction).

  • Tunica Externa: The outer layer made of loose connective tissue that helps hold blood vessels in place.

Page 7: Structure and Function of Arteries

  • What they're like: Arteries need to handle strong pressure from the heart, so they have thicker walls and smaller inner spaces (lumens) than veins.

  • Elastic Arteries:

    • Also called "conducting arteries," like the aorta and its main branches.

    • They have wide lumens to collect a lot of blood from the heart.

Page 8: Structure and Function of Muscular Arteries

  • Also called: "Distributing arteries."

  • What they're like:

    • They have the thickest middle layer (tunica media) of any blood vessel, allowing them to narrow very strongly (vasoconstrict).

    • They branch out a lot to send blood to smaller arteries (arterioles) all over the body.

Page 9: Structure and Function of Arterioles

  • What they are: Small branches of arteries.

  • Largest Arterioles:

    • Still have all three layers (tunics) and look like small muscular arteries.

  • Tiniest Arterioles:

    • Only have the inner lining (endothelium) surrounded by 1-2 layers of smooth muscle fibers.

Page 10: Diameter of Arterioles

  • What they do: They control how much blood flows into tiny blood vessel networks (capillary beds).

  • Resistance Vessels: Arterioles that can change their width to let more or less blood flow through.

  • Metabolic Responses:

    • They adjust blood flow based on what the local tissue needs.

    • Example: When you exercise, more NO (nitric oxide) is released, causing vessels to widen (vasodilation) to increase blood flow.

    • Example: Increased endothelins cause vessels to narrow (vasoconstriction) (this can cause a blood vessel spasm during blood clotting).

    • Both NO and endothelins are released by the inner lining of blood vessels.

  • Myogenic Responses: The smooth muscle in the middle layer (tunica media) automatically tightens or relaxes.

    • Example: If a vessel stretches or pressure increases, the muscle contracts.

Page 11: Structure and Function of Capillaries

  • What they are: The smallest blood vessels, so small that red blood cells have to go through in a single line.

  • What they do: This is where gases and nutrients are exchanged. They only have the inner lining (tunica intima), which is porous (permeable).

  • Most common capillaries don't have pores; exchange happens through gaps between cells and tiny pockets (pinocytic vessels).

  • Some have pores (fenestrations) in their endothelial cells to allow more fluid and larger molecules to pass.

  • Even bigger holes (fenestrations) and a broken basement membrane allow whole cells to move through.

Page 12: Fluid Exchange at the Capillaries

  • Hydrostatic Pressure: This is a pushing force that moves fluid and the things dissolved in it from a place of higher pressure to a place of lower pressure.

  • Osmotic Pressure: This is a pulling force that holds water molecules and dissolved substances together, mostly controlled by proteins in your blood like albumin.

  • When Fluid Leaves Capillaries: For fluid and dissolved molecules to leave the capillaries and reach the tissues, the pushing force (hydrostatic pressure) must be stronger than the pulling force (osmotic pressure).

    • Condition: \text{Capillary Hydrostatic Pressure} > \text{Osmotic Pressure} Capillary Hydrostatic Pressure

Page 13: Organization of Capillaries into Capillary Beds

  • Capillary Beds Definition: A network of tiny blood vessels (capillaries) that work together to exchange substances.

  • Parts of a Capillary Bed:

    1. Terminal Arteriole: Brings blood into the capillary network.

    2. Precapillary Sphincter: A ring of smooth muscle that helps control the pressure and amount of blood flowing into the capillaries.

    3. Capillaries: These are the vessels where exchange happens. They branch off a main path (metarteriole) and then come together to send blood back to a small vein (postcapillary venule).

    4. Anastomosis: A direct connection between two blood vessels that bypasses a capillary bed entirely.

    5. Postcapillary Venule: Carries blood away from the capillary network.

    6. Metarteriole: The central path running through the capillary network.

Page 14: Check-In Time!

  • Questions:

    • What parts do arteries have that veins don't?

    • What parts do veins have that arteries don't?

    • Is the pushing pressure (hydrostatic pressure) higher at the start (arterial end) or the end (venous end) of a capillary?

    • What did you learn?

Page 15: Structure and Function of Veins

  • Venules: Small blood vessels that carry blood from the capillaries back to the heart. They have all three layers (tunics) but they are very thin.

  • How Veins Form: Venules join together to form veins. Veins have wider inner spaces (lumens), so they are called "blood reservoirs" or "capacitance vessels" because they can hold a lot of blood.

Page 16: Composition of Veins

  • Valves in Veins:

    • Veins have much lower pressure than arteries.

    • To make sure blood flows back to the heart, wider lumens offer less resistance to blood flow.

    • Venous valves (special folds of the inner lining, tunica intima) make sure blood flows in only one direction.

Page 17: Venous Blood Pressure and Flow

  • Pressure in Veins: The pressure in veins is much lower than in arteries.

  • Muscular Pump:

    • Helps blood return to the heart. When skeletal muscles contract (squeeze), they press on the veins, increasing pressure and pushing blood towards the heart.

  • Respiratory Pump:

    • When you breathe in, the pressure in your chest cavity drops, which helps blood move towards your lungs and then to your heart.

Page 18: Focus on Disease: Varicose Veins

  • What they are: Happens when venous valves fail, causing blood to collect in the veins of the legs.

  • Causes:

    • Anything that stops blood from returning easily to the heart (e.g., pregnancy, being overweight, standing for long periods).

  • Symptoms:

    • Veins become stretched and swollen, possibly causing discomfort or pain, and sores (ulcers) can develop on the skin around them.

Page 19: Treatment for Varicose Veins

  • Varicose veins are usually not dangerous but won't go away by themselves.

  • Treatments:

    • Compression stockings can help with pain and stop them from getting worse.

    • Sclerotherapy: Injecting a solution to close the vein.

    • Lasers: Used to destroy the vein from the outside.

    • Catheter and Laser or Radiofrequency: Techniques to destroy the vein from the inside.

    • Ligation and Stripping: Surgery to tie off and remove veins.

    • Ambulatory Phlebectomy: Removing small veins through tiny cuts in the skin.

    • Insurance Coverage: Might cover treatments if there's pain or a health risk; usually not for cosmetic reasons.

Page 20: Angiogenesis

  • What it is: The creation of new blood vessels.

    1. Normal Blood Vessel: The starting point.

    2. Triggers for New Vessels: Damage, changes in blood pressure, or the need for more blood supply cause blood vessels to become more permeable (leaky).

    3. Growth Factors (GFs): Damage to membranes releases GFs that encourage cell division.

    4. New Out-folding: A tiny new sprout starts to form.

    5. New Blood Vessel: The new blood vessel grows and gets bigger.

  • Examples:

    • Can happen due to exercise, for natural healing, as a medical treatment, or with tumors (tumors use angiogenesis to grow).

    • Angiogenesis can be good (normal healing) or bad (tumor growth).

Page 21: Short-Term Regulation of Blood Pressure

Looks at how blood pressure is controlled quickly, unlike long-term control which is mostly handled by the kidneys (we'll talk about that later).

Page 22: Reminder on Fluid Dynamics

  • Blood Volume and Resistance: How much blood there is affects how much friction (resistance) it meets in blood vessels.

  • Heart Rate and Stroke Volume: These two things together determine cardiac output (how much blood your heart pumps per minute).

  • Relationships: Cardiac output and resistance both influence blood pressure.

Page 23: Nervous Control of Blood Pressure: Baroreceptors

  • How Baroreceptors Work:

    • These sensors send more signals to the brain's control center when they are stimulated (e.g., by high blood pressure).

    • Control Center: The part of the brain that slows the heart (cardioinhibitory center) gets excited, while the parts that speed up the heart (cardioacceleratory) and tighten vessels (vasomotor centers) are slowed down.

    • Effects on Blood Pressure:

    • Increased cardiac output (blood pumped by the heart) and total peripheral resistance (total friction in vessels) will lead to higher blood pressure.

    • Reflexes control your heart rate, how strongly your heart beats, and how much blood vessels tighten.

    • In contrast, fewer signals mean baroreceptors are less stimulated, allowing the heart-speeding and vessel-tightening centers to become active, which can result in a slower heart rate, weaker heart contractions, and lower overall blood pressure.

Page 24: Other Methods of Blood Pressure Control

  • Chemoreceptors: These sensors check levels of oxygen, carbon dioxide, and H+ in the blood. They help adjust how much blood the heart pumps and blood pressure to meet the body's needs.

  • Higher Brain Centers: Parts of the brain like the cerebral cortex and hypothalamus share information and communicate with the limbic system (which deals with emotions).

  • Hormones:

    • Anti-diuretic hormone (ADH): Also called vasopressin; makes blood vessels narrow.

    • Epinephrine and Norepinephrine: Make blood vessels narrow.

    • Oxytocin: Makes blood vessels widen.

    • Dopamine: In small amounts, it widens vessels, but in large amounts, it narrows them.

Page 25: Homeostatic Imbalance: Hypertension

  • What it is: A significant increase in blood pressure.

  • Dangers of High BP:

    • Higher risk of coronary artery disease (heart artery problems), heart attack, heart failure, vision loss, brain problems, and aneurysms (weak spots in blood vessel walls).

  • Causes:

    • Many things can lead to high blood pressure, including lifestyle choices, medicines, and not enough exercise.

  • Stages of High BP:

    • Normal: 120/80120/80 mmHg

    • Elevated: 120−129120-129 (systolic) over 8080 mmHg (diastolic)

    • Stage 1: 130−139130-139 (systolic) over 80−8980-89 mmHg (diastolic)

    • Stage 2: More than 140140 (systolic) over more than 9090 mmHg (diastolic)

    • Hypertensive crisis: More than 180180 (systolic) over more than 120120 mmHg (diastolic) (emergency).

  • Treatment:

    • Lifestyle changes and medicines to relax the heart/vessels or widen vessels. These include ACE inhibitors, beta-blockers, calcium channel blockers, nitroglycerin, and diuretics.

Page 26: Homeostatic Imbalance: Hypotension

  • What it is: When blood pressure is too low (usually diagnosed when it's below 90/6090/60 mmHg or causing symptoms).

Page 27: Circulatory Shock

  • Symptoms:

    • Pale and/or bluish skin, cold and sweaty skin, fast pulse and breathing, dizziness, weakness, nausea, vomiting, fainting, large pupils, anxiety, or feeling agitated.

  • Types of Shock:

    • Vascular Shock: Low blood pressure because blood vessels are too wide (e.g., from severe infection, septic shock).

    • Cardiogenic Shock: The heart can't pump enough blood, often due to a heart attack.

    • Hypovolemic Shock: Low blood volume, which can happen from severe bleeding or not enough fluids (dehydration).

  • Treatments:

    • Emergency oxygen, stopping blood loss (for hypovolemic shock), keeping the person warm (blankets), elevating feet (when helpful), giving blood thinners, and medicines to make the heart beat stronger; drugs that narrow blood vessels might also be used.

Page 28: Edema

  • What it is: Swelling caused by too much fluid building up in body tissues.

  • Causes:

    • Many life events or habits like sitting or standing for too long, eating too much salt, PMS, pregnancy, lack of protein, and certain medications (e.g., NSAIDs, blood pressure medicines, steroids, and some diabetes medicines).

  • Dangers:

    • Pain or trouble walking and damage to blood vessels and skin; mild cases might not have noticeable effects.

  • Treatments:

    • Compression and raising the affected area, massage, moisturizing skin, lifestyle changes, water pills (diuretics), and adjusting medications.

Page 29: Effect of Aging on Circulation

  • How Age Affects Blood Vessels:

    • Blood vessels become stiff and narrow because they lose their stretchiness, become less flexible, and fatty deposits (plaques) build up.

    • Stiff blood vessels contribute to higher average arterial pressure (MAP), which makes them even stiffer – a bad cycle.

  • Risks:

    • Increased risk of heart attack; women after menopause lose the heart-protecting effects of estrogen.

Page 30: Check-In Time!

  • Questions:

    • What are muscular and respiratory pumps?

    • What is a typical healthy blood pressure reading?

    • What makes blood vessels narrow as we get older?

Page 31: Major Blood Vessels of the Body

  • Important to Know: You should recognize these vessels and which specific body parts they supply blood to.

Page 32: Arteries and Parts of the Aorta

  • Main Artery Structures:

    • Aortic Arch

    • Ascending Aorta (goes up from the heart)

    • Thoracic Aorta (in the chest, behind the heart)

    • Descending Aorta (goes down, also behind the heart)

    • Abdominal Aorta (goes through the belly)

  • Note: The thoracic and abdominal aortas are parts of the descending aorta, separated by the diaphragm muscle.

Page 33: Arteries Branching from the Aorta

  • Main Branches:

    • Right Subclavian Artery

    • Brachiocephalic Artery

    • Right Common Carotid Artery

    • Left Common Carotid Artery

    • Left Common Subclavian Artery

  • Note: There is no Brachiocephalic Artery on the left side.

Page 34: Arteries of the Head and Neck

  • Important Head and Neck Arteries:

    • Anterior Cerebral Artery

    • Middle Cerebral Artery

    • Ophthalmic Artery (supplies the eye)

    • Circle of Willis (a loop of arteries in the brain)

    • Carotid Canal (a tunnel for an artery)

    • Posterior Cerebral Artery

    • Basilar Artery

    • Internal Carotid Artery

    • Carotid Sinus

    • Vertebral Artery

  • Branches of the External Carotid:

    • Superficial Temporal

    • Maxillary

    • Occipital

    • Facial

    • Lingual

    • External Carotid

    • Common Carotid Artery

    • Brachiocephalic Trunk

Page 35: Arteries of the Brain: Circle of Willis

  • Parts of the Circle of Willis:

    • Posterior Cerebral Artery

    • Anterior Communicating Artery (connects the right and left sides)

    • Posterior Communicating Artery

    • Anterior Cerebral Artery

    • Basilar Artery

Page 36: Arteries of the Arm

  • Important Arm Arteries:

    • Brachial Artery

    • Axillary Artery (in the armpit)

    • Ulnar Artery (on the pinky side of the forearm)

    • Radial Artery (on the thumb side of the forearm)

    • Superficial Palmar Arch (in the hand, closer to the surface)

    • Deep Palmar Arch (in the hand, deeper)

Page 37: Arteries of the Torso

  • Key Torso Arteries:

    • Renal Artery (Left) (to the left kidney)

    • Celiac Trunk (supplies stomach, liver, spleen)

    • Common Iliac Artery (Right) (branches in the pelvis)

    • Superior Mesenteric Artery (supplies small intestine and part of large intestine)

    • External Iliac Artery (Right) (continues to the leg)

    • Inferior Mesenteric Artery (Left) (supplies large intestine)

    • Internal Iliac Artery (Right) (supplies pelvic organs)

  • Note: The abdominal aorta is the main source for these arteries.

Page 38: Arteries of the Torso (Close-Up)

  • Branches from the Celiac Trunk:

    • Hepatic Artery (to the liver)

    • Splenic Artery (to the spleen)

    • Left Gastric Artery (to the stomach)

  • These branches are related to the abdominal aorta (descending aorta).

Page 39: Arteries of the Leg

  • Important Leg Arteries:

    • Popliteal Artery (Posterior) (behind the knee)

    • Femoral Artery (in the thigh)

    • Dorsalis Pedis Artery (on the top of the foot)

    • Anterior Tibial Artery (in the front of the lower leg)

  • Note: The leg's arteries are a continuation of the external iliac artery.

Page 40: Veins and the Vena Cava System

  • Important Vessels and Heart Parts:

    • Superior Vena Cava: A large vein that brings blood from the upper body back to the heart.

    • Inferior Vena Cava: A large vein that brings blood from the lower body back to the heart.

    • Pulmonary Artery: Though listed here in a section about veins, this is an artery that carries blood from the heart to the lungs.

    • Vena Cava: These large veins drain blood into the right upper chamber (atrium) of the heart.

    • Brachiocephalic Veins: Veins in the upper chest that merge.

    • Aorta: Though listed here in a section about veins, this is the main artery that distributes blood from the heart to the rest of the body.

    • Lung: The organ where gas exchange happens.

    • Right Atria, Ventricle, and Left Atria, Ventricle: The chambers of the heart.

Page 41: Veins of the Neck

  • Essential Veins:

    • Internal Jugular Vein: Major vein inside the neck.

    • Subclavian Veins: Veins under the collarbones.

    • Brachiocephalic Veins: Formed when the internal jugular veins merge with the subclavian veins.

    • External Jugular Vein: Vein on the outside of the neck.

Page 42: Veins of the Head

  • Key Head Veins (Sinuses): These are special venous channels in the brain:

    • Straight Sinus

    • Confluence of Sinuses (where several sinuses meet)

    • Transverse Sinus

    • Great Cerebral Vein

    • Sigmoid Sinus

    • Superior Sagittal Sinus

    • Inferior Sagittal Sinus

    • Superior & Inferior Petrosal Sinus

Page 43: Veins of the Arm

  • Key Arm Veins:

    • Brachial Vein (in the upper arm)

    • Axillary Vein (in the armpit)

    • Radial Vein (on the thumb side of the forearm)

    • Median Cubital Vein (often used for blood draws, in the elbow)

    • Ulnar Vein (on the pinky side of the forearm)

    • Palmar Venous Arches (Deep and Superficial) (in the hand)

    • Cephalic Vein (runs along the outside of the arm)

    • Basilic Vein (runs along the inside of the arm)

Page 44: Venipuncture and the Median Cubital Vein

  • What is Venipuncture: Sticking a needle into a vein to get blood or give injections.

  • Median Cubital Vein: Most commonly used for this because it's usually large and stable, though other veins can also be used.

Page 45: Veins of the Torso

  • Key Torso Veins:

    • Renal Vein (from the kidney)

    • Common Iliac Veins (in the pelvis)

    • External Iliac Veins (a continuation of the femoral vein from the leg)

    • Internal Iliac Veins (from pelvic organs)

Page 46: Vessels of the Liver

  • Blood Supply to the Liver:

    • The hepatic artery (comes from the celiac artery) brings oxygen-rich blood.

    • The hepatic portal vein brings blood rich in nutrients (and toxins) from the intestines, spleen, pancreas, and gallbladder.

    • The hepatic vein carries blood away from the liver to the vena cava.

Page 47: Veins of the Leg

  • Important Leg Veins:

    • Femoral Vein (in the thigh)

    • Great Saphenous Vein (a long vein on the inside of the leg)

    • Popliteal Vein (behind the knee)

    • Tibial Veins (Anterior and Posterior) (in the lower leg)

    • Dorsal Venous Arch (on the top of the foot)

    • Deep Plantar Venous Arch (on the bottom of the foot)