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
