Physiology Revision - Blood vessels Flashcards
How do arterioles change the flow of blood to capillaries? How are they different from arteries?
Arterioles are resistance vessels that control the flow of blood. Their pre-capillary sphincters constrict to reduce BF to caps, or dilate to increase BF.
Arteries in comparison are low-resistance vessels that serve as conducting vessels
What is active hyperemia?
The increase of BF according to the metabolic needs of the tissue
What is flow autoregulation?
The ‘maintenance’ of BF when driving pressure changes
- Pressure drops = vessels dilate
- Pressure increases = vessels constrict
Ex. Arterial pressure in organ drops, dilation occurs
What are some examples of things that cause vasodilation?
- Metabolites ex. CO2
- Tissue hypoxia (low O2)
- Decrease in pH
- presence of potassium, adenosine (ATP), nitric acid, bradykinin
What is the intrinsic property of smooth muscle in arteries that allows it to maintain a relatively constant BF? Explain how this works?
Myogenic regulation of arterial diameter
- When the pressure in an artery increases, the stretch of the artery increases, causing vasoconstriction to maintain flow
What are the three controls that affect the arteriolar smooth muscle diameter?
Hormonal controls
- Release of epinephrine from the adrenal medulla can cause vasoconstriction or dilation depending on what receptor it binds to
- Vasopressin (ADH) causes vasoconstriction to keep/reabsorb water
- Atrial natriuretic peptide vasodilates in response to stretching of the atria sensed by artrial myocytes
Local controls
- Myogenic autoregulation for vasoconstriction
- Presence of metabolites, or tissue hypoxia for vasodilation
Neural controls
- Vasoconstriction; Sympathetic nerves that release norepinephrine
- Vasodilation; neurons that release nitric oxide
Describe velocity in the capillaries
Slow to allow for diffusion across the thin membrane
Surface area dictates the rate of diffusion rather than the size of the capillaries
What are the three types of capillary endothelial arrangements?
Continuous - tightly regulated ex. muscle, nerve, fat, lymph node cells
Fenestrated - open or closed, bigger gaps for generous exchange in the renal system, glands and intestines
Discontinuous - Big gaps that are so loosely structured that blood cells can pass through
ex. liver, bone marrow, spleen
What are the three kinds of transport through capillary walls?
Bulk flow - seen in fenestrated capillaries with water and solutes
Vesicle transport - seen in continuous capillaries; engulfing proteins, fusing, then releasing on opposite side
Diffusion - Seen in continuous capillaries; only gases can freely cross (O2 and CO2)
What are the two kinds of pressures that control fluid balance at the capillary level?
Hydrostatic pressure; forces fluids out of the capillaries
Colloid osmotic pressure; helps bring fluid into the capillaries and maintains blood pressure in the capillary bed during metabolic exchange (large molecules stay in capillary bed)
When does filtration occur? When does absorption occur?
Filtration occurs when hydrostatic pressure exceeds colloid osmotic pressure
Absorption occurs when colloid osmotic pressure exceeds hydrostatic pressure
What are the core differences between veins and arteries?
- Veins have valves
- Thinner walls
- Less elastic tissue, less smooth muscle
- More distensible
- Lie closer to the skin
Veins are a blood resevoir. True or false?
True. Veins contain more than 60% of the total blood volume, compared to less than 15% in the arteries.
Veins average pressure is abt. 10mmHg
What determines venous pressure?
The difference btw Central Venous Pressure and Right Atrial Pressure
Veins do not actively constrict and and there pressure is low and non- pulsatile
How do veins change their compliance to blood?
Just like with arteries, veins use the same mechanisms as arterial diameter regulation: Neural, hormonal and local/endothelial factors
