Cardiovascular L7: Blood vessel properties cont.; lymphatic system Flashcards
What is the function of capillaries?
sites of exchange
Exchange occurs across capillary walls by _________ – no carrier-mediated transport systems (except for the blood-brain barrier)
diffusion
What are 3 ways diffusion can be increased?
- Minimal distance
- Maximal surface area
- Maximal time
How can minimal distance in capillaries be a way that diffusion can be increased? List 3 reasons
- Single layer of endothelial cells
- Thin wall (1 μm) & small diameter (7 μm)- red blood cells are 8 μm = (push plasma against walls)
- Proximity to cells
How can maximal surface area of capillaries be a way that diffusion can be increased?
High numbers (10-40 billion) = 600m2
How can maximal velocity in capillaries be a way that diffusion can be increased?
Velocity is slow due to extensive branching
What is flow rate?
volume of blood per unit of time
What is flow velocity?
distance of blood travelled per unit of time
Flow rate is _____ at all levels of vascular tree - CVS is a ____ loop so the volume of blood, (i.e. the flow rate), must ____ the CO (~5L/min at rest)
stable; closed; equal
Flow velocity _____ at all the levels of the vascular tree – it is ______ (directly proportional/inversely proportional) to the total cross sectional area of all vessels
varies; inversely proportional
How does the the structure of arteries and capillaries change? What effect does that have?
Has a larger CSA
What are 3 characteristics of capillary permeability?
- Endothelial cells fit together like a jigsaw to form the capillary wall
- The majority of capillaries have tightly joined endothelial cells with narrow water-filled spaces between them
- This allows for passage of small water-soluble substances
________ cells fit together like a jigsaw to form the capillary wall
Endothelial
The majority of capillaries have tightly joined ____ cells with narrow ______ spaces between them
endothelial; water-filled
The tightness of endothelial cells fit varies between organs. True or false.
True
In the cerebrum, how does the tightness of the endothelial cell fit vary?
tight junctions so no clefts are present –> blood-brain barrier
In skeletal muscles and lung (and most other), how does the tightness of the endothelial cell fit vary?
water-filled clefts (4nm) –> small, water soluble substances pass (ions, glucose, amino acids) but large water-soluble substances cannot (proteins via vesicular transport)
In the kidneys and intestines, how does the tightness of the endothelial cell fit vary?
Called reconditioning organs
water-filled clefts + fenestrations (20-100nm) –> ‘leaky’ capillaries (allow molecules to move through quickly)
In the liver, how does the tightness of the endothelial cell fit vary?
water-filled clefts (10-1000nm) + fenestrations (not between endothelial cells- there are holes within the endothelial cells) –> very large inter- &intra-cellular spaces, known as sinusoids
The liver is the site of protein formations (which are very big and can’t go through the water-filled clefts)
What are reconditioning organs or organs that get excess blood?
- Intestine
- Kidney
- Liver
What are sinusoids?
very large inter- and intra-cellular spaces
What are fenestrations?
Holes that are within the endothelial cells (not between the endothelial cells)
What are 4 characteristics to control blood flow through capillaries?
- No smooth muscle
- Pre-capillary sphincters are smooth muscle cells that spiral capillaries: myogenic tone (not innervated) & sensitive to local metabolic factors
- If metabolic activity increases, sphincters relax –> increase flow
- If metabolic activity decreases, sphincters contract –> flow is bypassed
What are the 2 main factors that blood flow through an organ is regulated by? What are the other 3?
- Number of open capillaries
- Degree of arteriolar resistance
- radius (only one that changes- out of the 3)
- viscosity
- length
What is interstitial fluid?
a component of ECF- space between blood vessels and cells within an organ (tissue)
What are 2 components that make up ECF? What is the percentage of each?
- Interstitial fluid (80%)
- Plasma (20%)
Movement between blood and cells is not direct. What are the 2 features?
- Movement in or out of cells can be passive or active
- Movement in or out of capillary endothelial cells is mostly passive (move down a concentration gradient)
- similar composition between arterial blood & interstitial fluid, except proteins
What are the 2 mechanisms that the exchange between blood and organs can occur?
- Diffusion
- Bulk flow
What is diffusion?
allows for individual solute exchange between blood & cells
Diffusion is ___ (active/passive) and goes __ (up/down) a concentration gradient.
passive; down
In this picture, explain what happens to glucose, O2 and CO2?
Glucose INTO cell:
- Passively diffuses down its concentration gradient (from plasma)
- to interstitial fluid
- Enters cells via glucose transport on surface of membrane
O2 INTO cell:
- Passively diffuses down its concentration gradient (from plasma)
- to interstitial fluid
- Enters cells via glucose transport on surface of membrane
CO2 OUT OF cell:
- Exits out of cell
- to interstitial fluid
- Goes into the plasma
______regulates distribution of ECF between plasma & interstitial fluid, i.e. maintains plasma volume
Bulk flow
What is the function of bulk flow?
regulates distribution of ECF between plasma & interstitial fluid, i.e. maintains plasma volume
What does bulk flow not play a major role in?
individual solute exchange
What are 2 types of pressures that influence bulk flow via ultrafiltration and reabsorption?
- Hydrostatic pressure
- Oncotic pressures
Protein free plasma flows out of capillaries and mixes with ______ and is then _____.
interstitial fluid; reabsorbed
Hydrostatic & oncotic pressures influence bulk flow via ______& ________. What are 2 things that are related to this?
ultrafiltration; reabsorption
- Capillary blood pressure &plasma proteins
- Interstitial fluid & proteins
What is ultrafiltration?
Fluid goes out
What is reabsorption?
Fluid comes in
if the interstitial fluid is too low in capillaries, what is a compensatory technique?
Interstitial fluid will flow in to compensate
Capillaries are the only vessels that have ___________. What does that allow?
‘pores’
to allow fluid to pass through
In the context of bulk flow, what would happen in response to a haemorrhage (severe blood loss- blood out of capillaries)? (Hint: a reduction in plasma volume reduces capillary blood pressure). What happens to ultrafiltration and reabsorption?
Net inward pressure is increased so fluid moves from interstitial fluid into plasma.
- Decreased ultrafiltration
- Increased reabsorption
What is the main function of the lymphatic system?
return excess fluid & protein that leaked out of capillaries back into the venous system
Acts as a back up to pick up the excess interstitial fluid and protein that hasn’t been absorbed.
What are the 2 other functions of the lymphatic system (apart from returning fluid)?
- Defense against disease
- Transport absorbed fat
What happens once it enters the lymphatic system? The relationship of the lymphatic system compared to the circulatory system.
What happens between blood flow and lymph flow?
What is oedema?
accumulation of interstitial fluid –> reduced exchange between blood & cells
What are 3 causes of reduced concentration of plasma proteins (abnormal physical force)?
- Kidney disease (increased protein in urine = less in plasma)
- Reduced liver function (should be response for proteins = less)
- Protein-deficient diet (not eating enough protein)
What is the cause of increased permeability of capillary walls (abnormal physical force)?
Histamine- inducing widening of pores (blisters and hives) Cause swelling, redness and increased fluid
What is the cause of increased venous pressure (abnormal physical force)?
backflow of blood in LL –> increase capillary hydrostatic pressure > extra ultrafiltration > extra fluid in ECF > oedema.
e.g. Pregnancy - growing uterus compress on veins, make it harder to return blood upwards. Also heart failure.
What is the cause of a blockage of lymph vessels (abnormal physical force)?
Surgical removal of nodes (or possible type of mosquito- rare) - difficult to take up lymph
