Davis: A and P, Peripheral Circulatory system

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Anatomy of Blood vessels, Physiology of movement of blood within blood vessels, and pathology of Blood Vessels

Blood vessels

networks of pathways for distribution of blood throughout the body

Layers of Blood Vessels

from inside out
1. Tunica Interna (Intima)
2. Tunica Media
3. Tunica Externa (Adventita)

Tunica Interna (Tunica Intima)

- lining of artery or vein directly exposed to blood.
- contains two layers
1. Endothelium - simple squamous epithelium and loose CT.
- releases vasocontrictors, vasodilators, and clotting factors

Tunica Media

- thickest wall of artery
- contains a layer of collagen with smooth muscle and elastic fibers
- capable of vasomotion
- acts as primary source of resistance to blood

Vasomotion

any change in diameter of Blood vessel

Vasoconstriction

contraction of blood vessel and constriction

Vasodilation

relaxation and expansion of Blood vessel

Tunica Externa (Tunica Adventita)

- merges with perivascular tissue of Blood vessel
- contains nerves and lymphatic vessels
- contains vaso vasorum

Vaso Vasorum

"vessels within vessels"
- they are small blood vessels on the walls that directly supple blood to larger blood vessels
- similar to the coronary circulation of the heart

Arteries

- efferent vessels that drain blood away from the heart
- resistance vessels
- strong resilient structure that withstands pressure exerted on it
- contains lots of smooth muscle in Tunia media and holds shape when empty

3 Categories of Arteries

1. Conducting (Elastic)
2. Distributing
3. Resistant (small arteries)

Conducting Arteries

- large
- located close to heart
- contains lots of elastic tissue to withstand large surges of blood and pressure
- capacity to handle changes in blood pressure

Some Conducting Arteries

1. Aorta
2. Pulmonary Trunk
3. Common Carotid
4. Common Iliac
5. Subclavian

Atherosclerosis

- reduced flexibility of arteries by hardening walls and produces strain

Results of atherosclerosis

- increased Blood pressure
- aneurysms

Aneurysm

- bulge in artery due to damage
- most common in abdominal aorta, renal arteries, and arteries at the base of the brain
- also caused by bacterial infections, like syphilis, any wall damage, or congenital weakness
- can occur in all BV and organs

Brain Aneurysms

- symptoms include: chronic cough, headaches, neurological issues, issues swallowing and breathing
- increased BP can cause a rupture producing a massive hemorrhage that can lead to sudden death.
- possibly operable

Distributing (Muscle) Arteries

- medium arteries
- contain large amounts of smooth muscle and has the thickest wall in the body
- distributes blood to organ and limbs

Some Distributing Arteries

1. Brachial
2. splenic
3. renal
4. femoral

Resistance (Small) Arteries

- contains more smooth muscle vs elastic
- variable and small, different in each body
- directly attach to arterioles

Arterioles

"little arteries"
- 40-200 um in diameter
- directly connect to metarterioles

Metarterioles

- channels that direct blood into capillaries

Precapillary Sphincter

access point between metarterioles and capillaries

Sense Organs with Arteries

1. Carotid Sinus
2. Carotid Bodies
3. Aortic Bodies

Carotid Sinus

inside carotid arteries
baroreceptors - monitor BP

Carotid Bodies

- in common carotid where external and internal branch off
- chemoreceptors - monitor O₂, CO₂, and blood pH
- stimulate increase and decrease in respiratory function

Aortic Bodies

- in aortic arch
- chemoreceptors

Veins

- Afferent vessels that carry blood to the heart
- capacitance vessels - stretchy to allow an influx of blood
- thin and flaccid, collapse when empty
- irregular shape which allows for greater capacity of blood flow
- have ↓cardiac pressure compared to other BV
- ↓ risk of aneurysms
- more blood contained in Veins
- smallest veins are farthest and converge onto bigger ones that connect to the heart

Tributary Veins

smaller veins that empty into bigger veins

Postcapillary Venules

- receive blood through thoroughfare channels or capillary beds
- smallest veins
- more porous than capillaries
- fluid exchange
- WBC exit through here

Muscular Veins

- veins that converge with venules and medium veins

Medium Veins

- contains venus valves
- converge with large veins
- found mostly in limbs

Venus Valves

- infoldings of endothelium
- prevents back flow of blood against gravity
- absent in thoracic, abdominal, cerebral veins

Some Medium Veins

1. radial
2. ulnar
3. saphenous

Varicose Veins

- bulging distending veins in lower extremities due to pooling of blood in those medium veins.
- stretches veins and wears out valves
- leads to edems

Causes of Varicose Veins

- prolong standing - movement and exercise will prevent
- obesity
- pregnancy
- congenital valvular weakness

Hemorrhoids

- varicose veins in the anus

Large Veins

- most muscular
- smooth muscle tissue in all three layers
- directly contacts with the heart

Examples of Large Veins

1. sup. and inferior vena cavae
2. Pulmonary veins
3. renal vein
4. jugular vein

Capillaries

- microscopic thin walled vessels that function to exchange gas to tissues
- interacts with arteries and veins
- exchange O₂, CO₂, Hormones, nutrients, and mobile cells like WBC
- contains no tunics only endothelium and basement membrane
- rare in tendons and ligaments
- not found in the cornea and lens of eyes, eithelial tissues, and cartilage

4 Types of Capillaries

1. Continuous
2. Fenestrated
3. Discontinuous
4. Capillary Beds

Continuous Capillaries

- contains tight gaps in walls due to tight junctions between endothelial cells, forming a tube
- contains Intercellular Clefts

Intercellular Clefts

- small gaps between tight junctions that allow small molecules through
- C₆H₁₂O₆, O₂, CO₂, elctrolytes, H₂O and other small molecules to diffuse through
- plasma proteins and hormones cannot pass through

Blood Brain Barrier

- continuous capillaries with no intercellular clefts within the brain

Fenestrated Capillaries

- small porous holes which allow small molecules to move through
- does not allow cells or platelets
- allow for rapid filtration and reabsorption

Organs that contain fenestrated capillaries

- kidneys
- small intestines
- endocrine glands
- Choroid Plexi

Discontinuous (Sinusoids) Capillaries

- largest capillaries that contains large fenestrations and gaps

Molecules that Pass through Sinusoids

- albumin
- clotting factors
- Monocytes can live in capillaries as macrophages
- RBC are moved from hemopoietic tissue to blood through sinusoids

Organs where Sinuosoids are Found

1. liver
2. Spleen
3. Bone Marrow
4. Thymus

Capillary Beds

- network of capillaries
- supplied with blood by a single metarteriole that travels along Thoroughfare Channel
- blood can either empty via venule or metarteriole that will empty into a venule
- precapillary sphincter regulates blood movement into capillary bed.
- 75% of beds do not have blood at a given time

Portal Systems

- blood moves through 2 capillary beds before moving into the vein for redirection to heart
- occur in places between 2 structures
- found in
Thymus
Hypothalamus to Pituitary Gland
liver to large intestine

Anastomoses

place where two blood vessels merge

Types of Anastomoses

1. Venous Anastomoses - vein to vein
2. Arterial Anastomoses - artery to artery
3. Arteriovenous Anastomoses (shunts) - vein to artery and vice versa

Arteriovenous Anastomoses

- found in extremities like toes, fingers
- used to bring blood to internally when its cold - maintains homeostasis

Blood Flow

amount of blood moving through a structure
= mL/min

Perfusion

amount of flow per mass of tissue
= mL/min/g

Blood Pressure

- force of blood on blood vessel walls
- measured as a proportion of systolic pressure/diastolic pressure
- average BP 120/75

Total Blood Flow

CO

Flow is affected by

1. BP
2. Resistance
3. Flow - ∆P/r (changes in systolic and diastolic pressure/resistance)

BP is measured by?

sphygmomanometer

Pulse Pressure

difference in pressure change during ventricular systole
- average PP 40mmHg

Mean Arteriole Pressure (MAP):

- average blood pressure per cardiac cycle
= 1/3PP + diastolic pressure
- MAP is higher at the areas closer to the heart

Chronic Hypertension

- ↑ BP
- 140/90
- strains on arteries
- causes aneurysms, strokes, heart attacks, clotts, and plaque buildup

Chronic Hypotension

- ↓BP
- anything<105-110/70
- caused by dehydration, anemia, massive blood loss, ↓ heart contractility
- causes fatigue, slow healing and slow removal of waster
- major drops can cause death

Causes of Arterial Pressure Change

1. CO - amount of blood pumped out of heart
2. Fluid Volume - regulated by kidneys
3. Peripheral Resistance (amount of resistance in BV flow)
4. Reduction of kidney function

Causes of Peripheral Resistance

1. Viscosity - blood thickness, buildup of RBS or proteins will affect viscosity
2. Radius of BV = Flow∞r⁴, small changes in radius will greatly affect flow
3. BV length - pressure and flow ↓ with ↑ in length

Hypoproteinemia

- lack of proteins in blood plasma causes the viscosity of blood to be thinner causing blood to move faster

Local Control

- Ability to increase and decrease blood flow in tissue
- kicks in during inflammation, trauma, exercise
- Metabolic Autoregulation Theory
- Reactive Hyperemia

Metabolic Autoregulation Theory

-achieved by vasoactive chemicals like histamine in endothelium
- inadequate perfusion causes hypoxia and increase in metabolites
- then BV vasodilate to bring in more O₂blood and takes away metabolites
- then BV constricts to bring back normal flow

Reactive Hyperemia

normal flow is restore to tissue, heat and blood return to deprived tissue

Angiogenesis

- growth of new BV
- stimulated by Hypoxia of loss of O₂
- commonly found in coronary ciculation

Angiogenesis can occur when?

- in inter uteri lining - after menstruation
- in development of adipose tissue
- rapid growth in tumors

Vasomotor Center

- Neural Control of blood flow directed by ANS
- sympathetic control of BV to cause vasoconstriction.
- coordinate reflexes that control flow

reflexes of Vasomotor Center

Chemoreflexes - responds to change in Blood chemistry
Baroreflexes - responds to BP
Ischemic Medullary Reflexes - auto reflexes of drops in perfusion within the brain (triggered by emotional stress and trauma)

Hormones that control Blood Flow

1. Angiotensin II
2. Aldosterone
3. Anti Natriuretic Peptide (ANP)
4. Anti Diuretic Hormone (ADH)

Affects of Angiotensin on Blood Flow

- vasoconstrictor

Angiotensin Converting Enzyme

- blocks hormone which causes vasodilation and ↑ in blood flow and ↓in pressure

Aldosterone

retains water which ↑ BP by blood volume

Anti Natriuretic Peptide (ANP)

- antagonist to Aldosterone
- commonly found in heart
- ↓ BP by getting rid of H₂O

Anti Diuretic Hormone (ADH)

- promotes water retention and vasoconstriction to ↑BP

Capillary Exchange

- movement of nutrients and gases out of blood and wastes gases into the blood.
- 2 way movement across Capillary walls

4 Mechanisms of Capillary Exchange

1. Diffusion
2. Transcytosis
3-4. Filtration and Reabsorption

Diffusion in Capillary Exchange

- small molecules like H₂O, O₂, and C₆H₁₂O₆ can move into tissue
- small molecules like CO₂ and wastes move out
- lipid soluble molecules can diffuse through
- H₂O molecules get transported by facilitated transport

Transcytosis

- movement of fluid into cell by pinocytosis, travels through cells via vesicle, and exits cells by exocytosis

Filtration and Reabsorption

At arterial end, materials flow out into capillaries and is delivers to tissues
At venule end, other material are absorbed
- driven by hydostatic and osmotic pressure

How does filtration cause Edema?

- most common cause is ↑ filtration and ↓ reabsorption
- due to kidney failure, age, poor venous return

Causes of ↓ filtration↑re-absorption

- Hypoproteinemia by sorosis of the liver, kidney diseases, severe burns, interference in lymphatic drainage

Mechanisms for Venous Return

1. Pressure Gradients
2. Gravity
3. Skeletal Muscle Pump
4. Thoracic (Respiratory) Pump
5. Venous Pooling
6. Cardiac Suction

Pressure Gradients

-small amounts of cardiac pressure get lesser as veins get smaller and farther from the heart
- occurs in venules
- 7-13mmHg will favor blood moving to the heart
- veins dilate - pressure ↑
- veins constrict - pressure↓

Skeletal Muscle Pump

- skeletal muscles squeeze on vein walls moving blood in 1 direction
- vein valves control circulation

Thoracic Pump

- aids flow between abdomen and thoracic cavity
- in inhalation, ↑in abdomen, and pressure in thorax causing expansion and pumps blood into vena cavae
- inhalation increases venous return faster than exhalation

Cardiac Suction

is the suction of Blood into the Rt. Atrium when the tendinous cords of the AV valves close and space is available

Venous Pooling

is the buildup of blood in the lower body due to the force of gravity when a person changes a position from sitting to standing

Extended Pooling

puts more pressure on BV to push blood to heart

Syncope

fainting, due to sudden change in position from laying to standing, prevents blood from going to the head

Circulatory Shock

- anything that causes CO and not keeping up with the body's needs
- can be cardiogenic - heart not keeping up with demand
- 1/2of people die from Circulatory shock

Types of Circulatory Shock

1. Low Veinous shock - blood not returning fast enough
2. Hypovolemic Shock - ↓ blood volume
3. Obstructed Venous Return Shock - block in vein due to aneurysm or tumor
4. Neurogenic - loss of vasomotor tone
5. Anaphylactic - antigen exposure (most common)
6. Septic Shock - bacteria in the blood

Compensated Shock

body recovers on its own
1. elevate feet above head
2. keep warm
3. Restore blood to head

Decompensated Shock

results in ischemia, myocardial infarction, blood clot, and death

Cerebral Ischemia

- Transient Ischemic Attack
- symptoms: dizziness, headache, blurry or loss of vision, paralysis, weakness, bouts of aphasia
- early signs of a stroke

Cerebrovascular Accident

- infarction of the brain tissue
- caused by atherosclerosis, thrombosis, and ruptured aneurysms
- leads to partial or complete blindness, paralysis, little or total loss of speech
- there are variable recoveries
- ranges are big and small

Exercise on Skeletal Muscle Flow

- flow increases with exercise
- reserves 1mL/min.
- ↑ will increase 20x
- causes vasoconstriction in other organs during exercise
- fatigue is much quicker during continued exercise rather than exercise with brief pauses

Flow to Lungs

- pulmonary arteries have little elasticity and contains↓ BP since they don't travel far
- Capillary Hydrostatic Pressure is ↑ in Pulmonary arteries than systemic veins
- systemic capillaries move slower to diffuse CO₂ and O₂
- ↓re-absorption ↑filtration, may cause Pulmonary Edema
- ability to redirect perfusion to other areas of the organ when there is damage, however it is usually progressive.

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