Structural basis of kidney function Flashcards
What is the importance of the kidneys?
Homeostasis
Why does a person drinking too much water have urine infections?
The kidney pumps out too much water and when they go to sleep they can’t drink anymore. Then in the morning they have concentrated urine which is more likely to get urine infection.
What are the functions of the kidney?
- filters the blood plasma (G)
- selective reabsorption (PCT)
- retention of unwanted contents in urine (LOH)
- concentration selection (DCT)
How is fluid lost?
Through exhalation, urine, sweat and faeces
What is the kidney sensitive to?
nerves and hormones
What is the endocrine function of the kidney?
Renin, erythropoietin
What happens during the process of filtration?
The glomerulus filters the blood and the filtrate only has small molecules
What happens during the process of reabsorption?
The materials are reabsorbed in the PCT, these include ions, glucose, amino acids, small proteins and water.
What happens during the creation of the hyperosmotic extracellular fluid?
The loop of Henle and vasa recta do this and the countercurrent mechanism is involved.
What are the mechanisms that occur during urine production?
- filtration
- reabsorption
- creation of hyperosmotic extracellular fluid
- adjustment of ion content in urine
- concentration of urine (CD)
What happens during the adjustment of ion content in the urine?
Happens at the collecting duct and DCT - the levels of Na+, K+, H+, NH4+ are adjusted
What is the renal corpuscle?
The Bowman’s capsule, glomerulus and podocytes
Blood supply in the renal corpuscle
At the vascular pole of the corpuscle from afferent arteriole to efferent creating a high pressure to filter
What does the filtration barrier consist of?
- Fenestrated endothelium
- Specialiased basement membrane
- Filtration slots between foot processes of podocytes
Where is filtrate drained from the renal corpuscle?
At the urinary polt of the corpuscle to PCT
How is urine concentrated
At the collecting duct water moves down its osmotic gradient and can be controlled by vasopressin
Proximal convuluted tubule functions
- Reabsorption of 70% of glomerular filtrate
- Na+ uptake by basolateral Na+ pump
- Water and anions follow Na+
- Glucose uptake by Na+/glucose cotransporter
- Amino acids by Na+/amino acid co-transporter
- Protein uptake by endocytosis
Proximal convuluted tubule structural features
- Sealed with (fairly water-permeable) tight junctions
- Surface area increased to maximise rate (at the brush border at apical surface
interdigitations of lateral membrane) - Contains aquaporins
- Lots of mitochondria
What happens in the ascending thick limb and why?
- Na+ and Cl- actively pumped out of tubular fluid
- Water impermeable tight junctions
- Membranes lack aquaporins
- Results in hypo-osmotic tubular fluid, hyper-osmotic extracellular fluid
Describe the structure of the descending thin limb
- Passive osmotic equilibrium (aquaporins present)
- Simple squamous epithelium
Describe the structure of the ascending thick limb
- High cuboidal epithelium, few microvilli
- prominent mitochondria
What is the vasa recta?
- Blood vessels arranged in loop
- Loop structure stabilises hyper-osmotic gradient [Na+]
Distal convoluted tubule - features, structure and role
- Cuboidal epithelium, few microvilli
- Numerous large mitochondria
- Loops back around to the glomerulus to form the juxtaglomerular apparatus (has macula densa cells)
Complex lateral membrane interdigitations with Na+ pumps - Adjustment of Na+/K+/H+/NH4+ (aldosterone)
Where does the CD pass through and what happens?
Where does it drain into?
- Passes through medulla with its hyper-osmotic extracellular fluid
- Completes ion adjustment
- Water moves down osmotic gradient to concentrate urine
- Drains into minor calyx at papilla of medullary pyramid
What does the rate of water movement depend on in the CD and what is it controlled by?
- On aquaporin-2 in apical membrane
- under control of vasopressin
- Basolateral membrane has aquaporin-3, not under control
What is the structure of the collecting duct?
- Duct has simple cuboidal epithelium
- Cell boundaries don’t interdigitate
- Has smooth muscle wall (2 layers) for peristalsis
- Little active pumping so fewer mitochondria
Juxtaglomerular Apparatus
Macula densa of distal convoluted tubule (detects Na+)
Juxtaglomerular cells of afferent arteriole which can detect pressure and secrete renin (angiotensinogen to angiotensin 1)
How can renal stenosis affect blood pressure?
renal stenosis - kidney think blood pressure had dcereased and makes renin causing high blood pressure
Where do aldosterone and vasopressin act?
DCT and CT
Which parts of the kidney are in the medulla and cortex?
cortex - DCT, PCT, CD and Bowman’s capsule
medulla - loop of Henle
What are some parts of the kidney?
cortex medulla (pyramids) fibrous capsule medullary rays minor calyces major calyces papilla of pyramid renal sinus renal pelvis fat in renal sinus vessels
Where does each lobe drain into?
Its own part of the renal pelvis called the minor calyx- they join to form the major calyx which drains into the ureter
How does urine get from the nephrons to the urethra?
minor calyx, major calyx, centre of pelvis and ureter, bladder, urethra
What is the special epithelium of the urinary tract and what is its structure?
urothelium
Has 3 layers of epithelial cells
What are the features of urothelium?
- 3 layers
- Urine facing (apical) side has high resistance tight junctions
- Apical side has thick membrane
These are important to minimise transepithelial migration - Urothelial cells have pleated borders to allow folding and unfolding depending on size of the bladder
How does the shape of the bladder and its location change when its full?
The empty urinary bladder is a small, muscular, tetrahedral organ lying below the pelvic peritoneum and not rising much above the
top of the pubic symphysis. As it fills with urine, it relaxes and expands upwards into the loose connective tissue between the deep surface of the anterior abdominal wall and the parietal peritoneum.
What does vesical mean?
structures relating to bladder
Which epithelium lines the glomerulus, PCT, loop of Henle (ascending and descending), DCT and CD?
Bowman’s capsule - simple squamous
PCT - cuboidal
Loop of Henle ascending - cuboidal
Loop of Henle descending - simple squamous
DCT - cuboidal
CD - cuboidal or columnar
Which epithelium do the minor/major calyces and pelvis have?
Urinary epithelium
What is urothelium or transitional epithelium, its features and where is it found?
- A specialised form of epithelium found only in the urinary tract: parts of kidneys, ureters, bladder, parts of urethra
- All cells contact basal lamina (but epithelium looks stratified)
- Properties are resistance to urine, and ability to stretch
- Cells appear squamous or cuboidal according to degree of stretch
- Luminal cells are specialised for extremely low permeability
