BLG600 cardiovascular system part 3: blood vessels

name the 3 types of blood vessels

* arteries
* veins
* capillaries

name the 3 layers of blood vessels and how they relate to each type of blood vessel

* Endothelium: simple squamous epithelium
* A, V, C
* smooth muscle and elastin
* arteries have lots of both, veins have lots of muscle but little elastin and capillaries have neither
* collagen fibers
* A, V, C

role of collagen in blood vessels

reinforces blood vessels

why is it important that the blood vessel’s endothelium is simple/one layer?

to allow diffusion of nutrients

what to blood vessels use to contract?

smooth muscle

role of capillaries

Supply blood to almost every cell in body (but not epithelia , cartilage or parts of eye

list and describe the different types of arteries

Elastic Arteries:

* largest arteries, take blood out of heart (like aorta, aortic arch, thoracic aorta, abdominal aorta) so also called conducting arteries
* have the highest BP because they are so close to the heart
* Contain the most elastic so are like elastic tubes that expand and recoil as blood is ejected

Muscular arteries:

* called distributing arteries bc they deliver blood to organs
* Lots of smooth muscle, less elastic, active in vasoconstriction
* branch off of aorta

Arterioles:

* Smallest arteries
* Mostly smooth muscle that controls flow into capillary bed thru vaso-constriction and dilation

what component of arteries moves the blood down the aorta?

elastic recoil

what happens in capillary beds?

* Blood flows from the arterial to venous end, releasing into- or absorbing molecules from- IF
* Substance Diffusion into or out of follows concentration gradient.
* Out of capillaries: Oxygen, amino acids, glucose, nutrient to IF
* Into capillaries: CO2, wastes
* More water leaves at arterial end than is absorbed venous end bc BP is slightly higher at arterial end
* Lymphatic system reabsorbs fluid (water, bacteria, cancer cells) and returns it to vascular system

why do salt and plasma proteins stay in the blood rather than diffusing out in capillary bed?

* salt stays in because it is too concentrated out of the blood vessel (staying in the blood vessel follows the concentration gradient)
* plasma proteins are too big to diffuse out

describe the anatomy of small and large veins

* largest layer?
* thickness of walls

Largest layer is the collagen layer, so thin walls but blood pressure in veins is low

Four adaptations that help veins return blood to heart

1. Valves prevent blood from flowing backwards in veins (next slide)

* Mostly in limbs, where blood is moving against gravity


2. Muscular pump: contraction of skeletal muscles “milks” blood back toward heart; valves prevent backflow
3. Respiratory pump: during breathing

* abdominal pressure increases, squeezes abdominal veins and moves blood toward heart
* At same time, pressure in chest decreases, thoracic veins expand speeding blood entry into right atrium


4. Sympathetic venoconstriction: under sympathetic control, smooth muscles of veins constrict, pushing blood back toward heart → normal maintenance

why does venous blood need help returning to the heart

because BP is so low in veins (near zero)

how does the size of blood vessels change as you move back up to the heart?

small away from the heart → large near the heart

what happens when vein valves do not work?

Varicose veins: leaky valves, veins become distorted and dilated and blood pools in lower limbs

Systolic pressure

Diastolic pressure

Systolic pressure: 120 mmHg. Maximum pressure felt in arteries when ventricles contract

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Diastolic pressure: 80mmHg. Ventricles relax, recoil pushes blood further into arterial system

short term regulation of BP

neural controls

* These alter resistance and cardiac output
* Ex: day to day maintenance of monitoring of blood pressure, during exercise

long term regulation of BP

renal controls

* These alter blood volume via kidneys

what happens when BP is too high?

* stimulus: BP is too high
* baroreceptors (stretch/mechanoreceptors) in carotid sinus and aortic arch are stimulated
* increased impulses from baroreceptors stimulate cardioinhibitory center and inhibit vasomotor center
* stimulating cardioinhibitory center decreases sympathetic impulses to the heart causing decreased HR, contractility and cardiac output (mL/min)
* leads to decrease in blood volume
* inhibiting the vasomotor center decreases the rate of vasomotor impulses which allows vasodilation and decreases resistance
* decreased cardiac output and resistance return BP to normal

what happens when BP is too low?

* stimulus: BP is too low
* baroreceptors (stretch/mechanoreceptors) in carotid sinus and aortic arch are inhibited
* decreased impulses from baroreceptors stimulate cardioacceleratory center (and inhibit cardioinhibitory center) and stimulate the vasomotor center
* stimulating cardioacceleratory center increases sympathetic impulses to the heart causing decreased HR, contractility and cardiac output (mL/min)
* leads to increase in blood volume
* stimulating the vasomotor causes vasomotor fibers to stimulate vasoconstriction causing increased resistance
* increased cardiac output and resistance return BP to normal

name the two mechanisms that kidneys use to regulate BP

1. Direct renal mechanism
2. Indirect renal mechanism (renin-angiotensin-aldosterone)

Direct renal mechanism for low BP

* stimulus: low BP
* indicates low water level in blood
* decreased filtration by kidneys
* decreased urine formation
* increased blood volume because more water is reabsorbed by blood vessels
* increased BP

\*kidneys regulate on their own without hormone interaction

general direct renal mechanism for decreased or increased BP

Decreased BP or blood volume causes kidneys to conserve water, and BP rises

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Increased BP or blood volume causes elimination of more urine, thus reducing BP

Indirect renal mechanism (renin-angiotensin-aldosterone)

* stimulus: decreased BP → inhibits baroreceptors → increased sympathetic nervous system activity
* increased renin release from kidneys: conversion of angiotensinogen to angiotensin I
* angiotensin I is then converted to angiotensin II
* angiotensin II
* goes to adrenal cortex to cause the secretion of aldosterone → increased sodium reabsorption by kidneys → increased water reabsorption by kidneys
* increases blood volume
* goes to posterior pituitary gland and causes increased release of ADH → increased water reabsorption by kidneys
* increases blood volume
* goes to hypothalamus to make you feel thirsty → increased water intake
* increases blood volume
* causes vasoconstriction and increases resistance
* Increased blood volume and resistance increases BP to normal