2.75

2.75 Recall that urine contains water, urea and salts

Urine contains water, urea and salts. Salt and water affect the concentration of tissue fluid (osmoregulation). The removal of urea is part of the excretion of metabolic waste. Concentration of urine depends on the condition of the body. 

2.74

2.74 Describe the role of ADH in regulating water content of the blood

The amount of water in your urine is controlled by a hormone called antidiuretic hormone (ADH); this is made by a gland in hypothalamus. It flows through the bloodstream and targets the kidney (collecting duct). ADH allows more water to come out of the collecting duct by making the walls more porous. The effect is to control and alter the composition or quantity of water in blood. ADH has the ability to make the blood more or less concentrated (tissue fluids must be isotonic with the cytoplasm of the cell).

Collecting duct is responsible for selective reabsorption of water and this is affected by the amount of ADH in the blood. The consequence of ADH secretion is more concentrated urine and lower volume.

When it is hot, more water would be lost as sweat so more ADH would be produced. When it is cold, less water would be lost so less ADH would be produced. When one is dehydrated, they want to keep the water in the body so more ADH would be produced. 


ADH makes the collecting duct more porous allowing more water to be reabsorbed into the bloodstream. 

2.73

2.73 Understand that selective reabsorption of glucose occurs at the proximal convoluted tubule

In PCT, glucose is removed and taken back into the blood. Glucose is selectively reabsorbed into the blood in the proximal convoluted tubule. Urine does not contain glucose. If glucose is in urine, this is an indication of diabetes.

2.72

2.72 Understand that water is reabsorbed into the blood from the collecting duct

During ultrafiltration, too much water is filtered. So the filtrate passes through the PCT to loop of Henle. When it reaches the collecting duct, water is removed from the filtrate. Water returned back to the blood vessels. Water has been selected and reabsorbed. Selected reabsorption of water occurs in the collecting duct. 

2.71

2.71 Describe ultrafiltration in the Bowman’s capsule and the composition of the glomerular filtrate

The nephrons filter blood and remove waste from the body. Waste consists of urine, which is largely water, salts and urea. At the beginning of the nephron (Bowman’s capsule), ultrafiltration begins. Blood arrives in the kidney in afferent arteriole (high pressure), which branches into blood vessels of the glomerulus. The blood vessel exiting is smaller in diameter, which means it has a high blood pressure. This forces the plasma and all the dissolved components (water, salts, amino acids, glucose and urea) into the Bowman’s capsule. The plasma is now called the glomerula filtrate. All these are filtered into the space inside of the Bowman’s capsule. Only the large plasma proteins remain in the blood and continue to the PCT. 

2.70

2.70 Describe the structure of nephrons, to include Bowman’s capsule and glomerulus, convoluted tubules, loop of Henle and collecting duct

Inside each kidney, there are thousands of tiny tubes called nephrons. They filter your blood and remove waste chemicals. Blood is brought to each kidney in the renal artery, which contains a lot of waste chemicals like urea. The artery branches many times, and each branch ends with a bunch of capillaries called a glomerulus. The glomerulus is inside part of the nephron called the Bowman’s capsule (double-walled, cup-shaped), the first part of the kidney tubule. As blood passes through each glomerulus, that large molecules like blood proteins can’t pass through while small molecules like urea, glucose, salts and water pass out of the glomerulus into the nephrons. This is because the filter is like a net with tiny holes. The leftover urea and waste salts are dissolved in water to produce urine. It flows down the ureter to the bladder. The clean blood leaves the kidney into the renal vein. 

Nephron: functional unit of the kidney that does the filtration and controls the composition of the blood.

Aorta à Renal artery à blood into the kidney à the kidney filters the blood à Urine removed from blood à comes down the ureter à collects in the bladder for release

(Other cleaned blood enters the renal vein into the vena cava.)

The space in the middle is known as the pelvic region (NOT THE SAME AS PELVIS). Urine gets collected in this area and drains down the ureter.

They are labelled in different colours because the kidney is made up of millions of tubular structures.

The tubes are twisted into sections known as proximal (first twist) and distal (second twist) convoluted tubules (aka PCT and DCT).

The arrangement of the tubules gives the different colours in the kidney. There are millions of tubules of nephrons in a kidney.