Flashcards in Chapter 10 - Homeostasis Deck (63)
What are the main functions if the excretory system?
1. Blood pressure
2. Blood osmolarity
3. Acid-base balance
4. Removal of nitrogenous wastes
What do AFFERENT and EFFERENT arterioles do?
Afferent arteriole: goes from the artery through the medulla and to the cortex
Efferent arteriole: lead blood away from AFFERENT arterioles to the second capillary bed.
What structures does the blood pass through in the kidneys / to get through the nephron?
Glomerulus / Bowman's capsule
(First capillary bed)
(Second capillary bed) - "vasa recta"
Proximal convoluted tubule
Loop of henle
Distal convoluted tubule
What is the vasa recta?
The capillaries that surround the loop of henle (second capillary bed)
What is the DETRUSOR muscle?
Muscle associated with the internal urethral sphincter
Stretch receptors detect bladder is full
Parasympathetic neurons fire
Detrusor muscle CONTRACTS
Internal sphincter relaxes
The contraction of the DETRUSOR muscle leads to the relaxation of the internal urethral sphincter
How does one urinate?
Voluntary control of external urethral sphincter
Urination is facilitated by the contraction of abdominal musculature, which creates pressure in the abdominal cavity and hence pressure on the bladder --> increases urinary flow rate
What is the MAIN role of the kidneys?
To regulate blood volume and osmolarity
What are the the main functions of the kidneys:
What is a portal system?
Consists of two capillary beds through which blood must travel before returning to the heart
What are the three main portal systems in the body?
1. Kidney portal system
2. Hypophyseal postal system (connects hypothalamus and ant pituitary)
3. Hepatic portal system (connects the gut tube and the liver)
WHAT IS (brief) filtration, secretion, and re absorption:
FILTRATION: movement of SOLUTES from the blood to the filtrate at Bowman's capsule
SECRETION: movement of SOLUTES from blood to filtrate anywhere but the capsule
REABSORPTION: movement of SOLUTES from filtrate BACK TO BLOOD
How is the glomerulus like a sieve?
Small molecules dissolved in the blood will pass through the tiny pores
Large molecules will not, and be removed into the urine
(Blood cells, proteins)
**Blood cells or proteins found in the urine indicate a problem with the glomerulus
What are Starling forces?
Results in the movement of fluid into Bowman's space
Account for the pressure differential between the blood and Bowman's space
(Account for both HYDROSTATIC and ONCOTIC pressure differences)
Hydrostatic pressure versus osmolarity in the glomerulus / Bowman's space
Hydrostatic pressure: higher pressure in the glomerulus so fluid wants to move to Bowman's space
Osmotic pressure: higher concentration of solutes in the glomerulus so fluid would want to move TO the glomerulus
BUT HYDROSTATIC PRESSURE IS MUCH GREATER
Usually, fluid flows from glomerulus to Bowman's space. What might cause de-arrangement of this?
Obstructed ureter (ie kidney stone)
How much (volume) of blood is filtered by the kidneys?
180 liters per day is filtered
This is about 36 times the amount of blood we have (4.7-5 L)
Aka, our entire volume of blood is filtered approx every 40 mins
What substances are typically reabsorbed from the filtrate?
ALSO A LOT OF WATER, ie ADH and aldosterone can alter quantity of water re absorbed at the kidney to maintain blood pressure
What substances are typically "waste" and not re absorbed?
Ammonia / urea
What happens at the PROXIMAL CONVOLUTED TUBULE?
(Closest to the capsule)
Of the things the body wants to keep
-water soluble vitamins
From the blood into the filtrate
-ammonia and urea
What is the interstitium?
What happens to solutes that end up here?
The connective tissue that surrounds the nephron
Solutes here are picked up by the vasa recta and hence returned to the blood
What happens at the DESCENDING LOOP OF HENLE?
Only permeable to water
Goes deep into the medulla, which has INCREASING osmolarity
Water flows out from the filtrate to the medulla (aka the interstitium) and goes to the vasa recta to go back into the blood
How can the kidneys change osmolarity in the medulla?
The medulla can be isotonic with blood (when the body wants to excrete water)
The medulla can be up to four times as concentrated (when it wants to conserve water and maximize reabsorption)
In order to get maximum reabsorption and conserve water
What is the COUNTER-CURRENT MULTIPLIER SYSTEM?
The flow of filtrate through the loop of henle is in the opposite direction as the flow of blood in the vasa recta.
This is to prevent equilibrium (if they both were going in the same direction) and allows max reabsorption of water!
What happens at the ASCENDING LOOP OF HENLE?
Only permeable to SALTS
Due to high concentrations of salt at the medulla and decrease as the loop goes up, salt moves out from the filtrate as it goes up.
Comment on the thickness of the loop of henle
Thickens as the ASCENDING loop moves to the outer medulla.
The loop itself not thicker but cells around it are larger and contain a lot f MITOCHONDRIA to actively transport sodium and chloride.
What is the diluting segment of the loop?
The thick portion
So much Na and Cl is re absorbed that the filtrate (urine) is more dilated than the blood!
This is the only place that this may happen
This is useful when over hydrated and needing to get rid of water
Filtrate at the beginning at the loop is isotonic to the interstitium. How does it compare at the end?
It is a bit more diluted (lower osmolarity than the interstitium)
What happens at the DISTAL CONVOLUTED TUBULE?
ALDOSTERONE can act on the DCT
Promotes reabsorption of sodium, and water tends to follow
Also, more waste secretion (like the PCT)