Excretion and Osmoregulation

• The kidney is involved in excretion and osmoregulation
• Excretion is the removal of metabolic waste
• Egestion involves the removal of undigested material
• Urea forms from deamination, the breakdown of amino acids

Osmoregulation in Unicellular Organisms

• Unicellular organisms like euglena or amoeba use contractile vacuoles for osmoregulation
• Osmosis occurs constantly in freshwater, a contractile vacuole collects excess water, releases it to the environment

The Urinary System

• The urinary system consists of the kidneys, ureter, urinary bladder, and urethra
• The system filters blood, creates, and removes urine from the body
• Kidneys produce urine, exits through the ureter to the urinary bladder for temporary storage, released through the urethra

The Human Kidney

• Humans have two kidneys located above the pelvic region
• The kidney filters blood to take up urea, excess salts, excess water, and excess hormones, forming urine
• The renal artery and renal vein bring and take away blood, respectively, to filter blood constantly
• The cortex and medulla are the two main regions in the kidney
• The cortex, the outer region, is where blood gets filtered
• The medulla, which is where urine is formed, is dark red and also where renal pyramids transport urine

The Nephron

• The nephron is where urine is produced; millions are in each kidney
• Nephrons are a series of tubes with a rich blood supply
• Selective re-absorption occurs in some parts of the nephron
• Selective re-absorption specifies re-absorption to chemicals in the blood
• The Glomerulus and Bowman's capsule are related to the nephron
• The renal artery divides into smaller blood vessels until it forms the glomerulus
• Blood enters through the afferent arteriole and exits through the efferent arteriole
• High pressure is maintained because the afferent arteriole is wider
• The glomerulus' blood capillary coils to form a dense network, helping to maintain high pressure for ultrafiltration
• Water, urea, glucose, amino acids, salts, and hormones pass into the Bowman's capsule
• Blood cells, platelets, and proteins do not pass through
• Bowman's capsule filtrate is the glomerular filtrate

Tubule Functions

• Selective re-absorption occurs in the proximal convoluted tubule as glucose and amino acids are actively transported by the blood
• The loop of Henle reabsorbs water back into the blood through osmosis, which helps regulate water
• The distal convoluted tubule reabsorbs salt, like sodium and chlorine ions
• The collecting duct contains urine and leads to the renal pelvis, ureter, and bladder

Osmoregulatory Function of the Kidneys

• Kidneys regulate water and salt levels by changing the amount of water removed with urine
• If there's too much water, the urine released is dilute
• If there's too little water, ADH (Antidiuretic hormone) signals the pituitary gland to increase water uptake from the collecting duct back to the blood, which concentrates the urine

The Dialysis Machine

• The dialysis machine filters blood for those whose kidneys no longer function properly
• During this process, blood passes next to a dialysis fluid
• The fluid contains a semi-permeable membrane which filters the blood of the patients' toxins
• The fluid would contain the same concentration of glucose and amino acids as the blood so that none is lost by diffusion
• Waste products then diffuse from the blood into the fluid and the "clean" blood is returned to the body