mix3 Flashcards
How many layers of smooth muscles do arteriole walls have?
Arterioles usually contain only one to two layers of smooth muscle in their walls
Where is the primary site of vascular resistance?
Arterioles
Where does the greatest change in in blood pressure and velocity of blood flow occur?
at the transition point between arterioles and capillaries
Describe the range of permeability profiles of the capillary beds
Blood-brain barrier: only gases and water can freely diffuse across the specialised endothelial layer in the brain
Sinusoidal: In liver- red blood cells can move in and out of the circulation
Fensetrations: In kidney- allow rapid water, small protein and molecule movement in and out of tissues
Describe the three layers of venule walls
An inner endothelium composed of squamous endothelial cells that act as a permeable membrane
a middle layer of muscle and elastic tissue ( poorly developed to have thinner walls that arterioles)
an outer layer of fibrous connective tissue
why is the porosity of venules particularly important in the anterior pituitary?
short portal venules between the neural and anterior pituitary lobes provide an avenue for rapid hormonal exchange via the blood.
What are high endothelial venules?
a special type of venule where the endothelium is made up of simple cuboidal cells
Which veins carry oxygenated blood to the heart?
pulmonary and umbilical veins
What is the role of valves in veins?
to prevent backflow, ensure unidirectional flow
important in the control of blood pressure as changes in the muscular tone of veins change central blood volume and thus blood pressure
what are the portal venous systems? Give examples
wo capillary beds are joined together by a series of veins or venules
hepatic portal vein and the hypophyseal-hypothalamic portal system in the hypothalamus and anterior pituitary
name the two sensors in the body and what they measure
skin and hypothalamus, which measure the external body temperature and the internal (core) body temperature, respectively
If the pH of blood falls below 7.35, then this is called….
acidosis
if pH increases above 7.45, then this is called…
alkalosis
Signs and symptoms to acidosis
headaches, confusion, feeling tired, tremors, and coma
What are the two types of acidosis
metabolic acidosis= increased production of metabolic acids, such as lactic acid or an inability to excrete acid via the kidneys
respiratory acidosis= an excessive buildup of carbon dioxide due to hypoventilation
What mainly determines the movement of water between compartments and across cell membranes
differences in hydrostatic and osmotic pressures on either side of these barriers
How are hydrostatic forces created?
by the pumping action of the heart
How are osmotic pressures created?
by the concentration of solute particles
how can osmotic pressure be measured?
from the number (concentration) of solute molecules present in a solution.
where is an increase in plasma osmolality detected?
hypothalamus
What is the protective mechanism used by the hypothalamus when there is a rise in plasma osmolality? Why is this important?
the sensation of thirst is quenched, preventing excessive consumption and encourages frequent small drinks until fluid balance is restored
if water is consumed too quickly (or if there is blockage of urine production) body fluids become diluted and there is a reduction of sodium concentration in the extracellular fluid that causes a shift in osmotic pressure making cells and tissues swell= oedema
What four categories can tissues be divided into?
epithelial tissue
connective tissues (includes blood, cartilage, bone, teeth and fat)
muscle tissue
nerve tissue
Describe the functions of epithelial tissue layers?
Protection: deeper layers of tissue from injury or infection, skin protects underlying tissues from sunlight, heat, cold, abrasion
Absorption/secretion: Nutrients from gut, secretion of enzymes for digestion
Selective diffusion: Transfer of gases, nutrients & waste products between blood and surrounding tissues
Name some roles of membrane transport systems
• Maintenance of intracellular pH
• Maintenance of intracellular ionic composition
• Regulation of cell volume
• Uptake and concentration of metabolic fuels and building blocks
• Extrusion of waste products of metabolism and toxic substances
- in some cases drugs
• Generation of ionic gradients necessary for the electrical excitability of nerve
and muscle
Define passive transport
Non-polar molecules are able to enter and, therefore, diffuse across the hydrophobic domain of lipid bilayers
Define permeability coefficients
the speed at which any substance transverses a lipid bilayer
What are the models for facilitated transport?
protein pores (also known as channels), ping-pong proteins (carriers) and flip-flop proteins (unlikely thermodynamically)
Whether the transport of an ion or molecule can occur spontaneously
(passive transport) or requires energy (active transport) is
determined by ….
the free energy change of the transported species
what is secondary active transport?
the transport of one substance is linked to the concentration
gradient for another substance via a co- transporter
Name some examples of cotransporters
Na+ glucose co-transport in the small intestine and kidney (symport).
Entry of sodium provides the energy for the entry of glucose
• Na+/Ca2+ exchange - Inward flow of sodium down its concentration
gradient drives outward flow of Ca2+ up its concentration gradient
(antiport)
•Na+/H+- exchange - Inward flow of sodium down its concentration
gradient leads to cell alkalization by removing
How does thiazides work?
Thiazides block the action of the sodium-chloride co-transporter
(NCCT) resulting in sodium retention (and hence water) in the collectingduct
how does ADH work?
Anti-diuretic hormone (ADH - also known as (arginine)-vasopressin [AVP]) acts on aquaporins to allow water to quickly back into the body
How does aldosterone work?
Aldosterone is a mineralocorticoid hormone produced by the adrenal cortex that acts as a nuclear transcription factor when it binds to the mineralocorticoid receptor. In the cortical collecting duct, aldosterone thus
stimulates the synthesis of ROMK, the epithelial sodium channel complex (ENaC) and the Na-K-ATPase (Na pump)
how does Amiloride work?
Amiloride blocks the action of the ENaC. Na+ stays in the duct and water stays with it and is passed in the urine, thus lowering water retention.
how does spironolactone work?
it antagonises the actions of aldosterone at the mineralocorticoid receptor, thereby preventing these
channels and transporters that move Na+ from the collecting duct into blood from being produced. Na+ stays in the duct and water stays with it and is passed in the urine, thus lowering water retention.
