Kidneys

Nephron

Unit of th ekidney which filters blood and produce urine

There are millions of nephrons per kidney

Name the parts of the kidney

Glomerulus

Bowman’s capsule

Proximal convoluted tubules

Loop of henle

Distal convoluted tubule

Collecting duct

Glomerulus

A cluster of capillaries found in bowman’s capsule

Ultrafilteration steps

Occurs in glomerulus

Blood enters glomerulus capillaries at high pressure (occurs as capillaries are narrower than arterioles that brings blood to nephrons)

Glomerulus capillaries are fenestrated, allows about 20% of blood plasma to leak out

Produced glomerular filtrate enters bowman’s capsule

Functions of glomerulus and ultrafiltration

Prevents large molecules from entering nephron

Many useful substances from blood plasma are in glomerulus filtrate, which can be reabsorbed by bloodstream as filtrate passes through proximal convoluted tubules.

Basement membranes

Glycoproteins which filters blood plasma

Bowman’s capsule function

Cup shaped structure that surrounds glomerulus, collecting glomerular filtrates.

Has 2 layers, with the outer layer made of simple squamous epithelium and visceral. Both composed of podocyte cells.

Adaptations of glomerulus

Capillaries with many pores within walls.

Proximal convoluted tubules

Reabsorb nutrients and water

Adaptations of proximal convoluted tubules (5)

• Folded and has microvilli on cells: Increase surface area

• 1 cell thick: Allows rapid transport

• Protein pumps: Selective active transport for nutrients

• Mitochondria: Many to produce ATP by aerobic respiration for active transport

• Surrounded by capillaries: Transports nutrients and water away from kidneys.

Selective reabsorption PCT

• All glucose & amino acids are actively transported out of the proximal convoluted tubules into capillaries

• 80% of minerals are actively transported out of the proximal convoluted tubules into capillaries

• High concentrations of solutes are outside tubules, causing 80% of water in filtrate to osmosis out the proximal convoluted tubules

Loop of Henle function

Located within medulla of kidney

Reduces volume of filtrate by transporting water and Na⁺ into medulla

Accending limb of Loop of Henle

Actively transports Na⁺ into medulla, impermeable to water

Creates high Na⁺ concentration in medulla, multiple nephrons all transporting Na⁺ into medulla

Medulla becomes hypertonic to the filtrate

descending limb of Loop of Henle

Has aquaporins and is permeable to water but not Na⁺. Water leaves by osmosis due to high concentration of Na⁺ into the medulla.

Distal convoluted tubules function

Balances:

1. pH of blood

2. Mineral concentration in body

Selective reabsorption and secretion DTC (what is transported, using what, why and how)

Absorbed ions: Na⁺, HCO₃^-

Secreted ions: K⁺, H⁺

Under the influence of hormones ADHH etc.

Secretes (blood to filtrate) H⁺ and absorbs (filtrate to blood) HCO₃^-: to maintain pH. (increase pH)

Secretes (blood to filtrate) Na⁺ and absorbs (filtrate to blood) K⁺: Conditionally reabsorbs Na⁺ , adapting to body’s needs. K⁺ secreted to maintain electrolyte balance.

Collecting duct

Where remaining filtrate goes (urine) readu to be excreted.

Osmoregulation

Maintenance of internal balance between water & dissolved materials by animals, regardless of environmental conditions

Kidneys regulate balance between blood, tissue fluid, and cytoplasm

Osmoreceptors

In hypothalamus (brain). Monitors osmotic concentration of the blood