Excretory System

Functions of the Kidney

• Excretion – Removal from the body of the waste products of metabolic pathways

• Osmoregulation – Is the control of the water balance of the blood, tissue, or cytoplasm of a living organism.

Draw and label a diagram of the kidney

Kidney Structure

Nephron – the functional unit of the kidney

Annotate a diagram of a glomerulus and associated nephron to show the function of

each part

Ultrafiltration specifics

• Production of filtrate from blood

• 20% of blood plasma passes through walls of glomerulus; higher than any other cap. bed.

• Why?

• 1. bp is very high due to diameter differences of the efferent and afferent arterioles

• 2. glomerular capillaries are fenestrated

• Pores large : all substances can pass through

• But basement membrane acts as a filter

Explain the selective reabsorption of glucose, water and salt in the PCT, including the roles of

microvilli, osmosis, and active transport

• Filtrate at this point contains waste and substances the body needs

• PCT consists of a single layer of cuboidal epithelial cells with microvilli = increased SA

PCT cont’d• IMPs all cell over surfaces for AT

• Mitochondria in large numbers producing ATP to drive AT

What’s Re-absorbed?

• 100% of glucose

• 80% of mineral ions (including Na)

• AT of solutes makes cell hypertonic

which cause water to follow.

• 80% of water is re-absorbed; 20% of water remains in the renal tubule and heads towards the LOH

Explain the role of the LOH, medulla, collecting duct (CD) and

ADH in osmoregulation• Descending and acsending limbs differ in

permeability.

• Major role?• To create an area of high solute conc. in the medulla

(hypertonic interstitial fluid)

Osmoregulation in the CD• Water conc. in blood too low =

• ADH release from pituitary gland in brain =

• Increase in aquaporin production in CD cells

• CD passes through zone of high solute conc created earlier by the LOH

• Hypertonic urine is produced

• If water conc in blood is too high (hypotonic blood) =

• ADH is not secreted =

• Aquaporins are broken down =

• CD becomes less permeable to water

• Dilute, hypotonic urine is produced

Explain the difference in the conc. of proteins, glucose, and urea between blood plasma,

glomerular filtrate and urine• The Urinary System• Plasma, Filtrate, and Urine ComparisonsTable. Average Composition

of Blood Plasma, Glomerular Filtrate, and Urine 

•   Blood Plasma Glomerular Filtrate Urine• Substance  (total amount) (amount per day) (amount per day)• Water 3 L 180 L 1-2 L

• Urea 4.8 g 53 g 25.0 g• Chloride 10.7 g 639 g 6.3 g• Sodium 9.7 g 580 g 4.6 g• Potassium 0.5 g 30 g 2.0 g• Creatinine 0.03 g 1.6 g 1.6 g • Uric acid 0.15 g 8.5 g 0.8 g• Protein 200.0 g 2.0 g 0.1 g• Bicarbonate 4.6 g 275.0 g 0.0 g • Glucose 3.0 g 180.0 g 0.0 g

Explain the presence of glucose in the urine of untreated diabetics