The excretory system

What are the functions of the kidneys

• primary excretory organs

Work to:

• ride body of wastes, especially nitrogenous wastes such as urea,Uric acid and creatine

• Maintain constant concentration of materials in body fluids

• Regulate the balance of fluid, salt & pH

How does the Kidney achieve those functions?

Filtering through blood as it passes through

Waste substances removed by process of filtration and tubular secretion

Useful substances returned to body by process of selective reabsorptiom

What is the structure of the excretory system?

Kidney 2x

Urinary bladed 1x

Ureters 2x

Urethra 1x

What is the structure of the kidney?

What is the Nephron?

• functional unit of the Kidney’s

• Make urine

• ~ 1.2 million nephrons in each kidney

What does ghe Nephron consist of?

• renal corpuscle (made of bowman’s capsule and glomerulus)

• Real tubule (divided into proximal convoluted tubule, loop of henle, and distal convoluted tubule)

• Associated blood supply

What is the renal corpuscle and what does it do? + it’s divisions

• filtration takes place in renal corpuscle

• Consists of bowman’s capsule ad mass of blood capillaries (called glomerulus)

• renal arteries delivering blood to kidneys are large, approximately 1.2L passes through the pair

• Renal corpuscle has afferent (in) and efferent (out) arterials

• Efferent arteriole then divide into network of pertubular capillaries surrounding Renal tubule

What are podocytes and what do they do?

• specialness cells that line bowman’s capsule

• Cells have finger-like extensions that wrap around capillaries of the glomerulus

• Spaces between the ‘fingers’ are filtration slits

How does filtration occur in the Kidney? stage 1

• occurs in glomerulus, where fluid is forced out of the blood, into bowman’s capsule

• Blood pressure within glomerulus high, aiding movement of fluid

How does filtration occur in the Kidney? stage 2

• Afferent (in) arteriole wider diameter than efferent (out) arteriole = increases resistance to blood flow and increases blood pressure, forcing water and s dissolved blood components out of the capillary

How does filtration occur in the Kidney? stage 3

• walls of glomerular capillaries ans the glomerular capsule are only 1 cell thick (and flat)

• Filtrate consists of the materials in the blood except red and white blood cells and plasma proteins (too large)

Filtration as a diagram

How does reabsorption occur in the Kidney?

• selective reabsorption of materials from the filtrate, required by body, takes place in renal tubule

• Returned to blood in pertibular capillaries

• Convolutions of renal tubule, and high number of nephrons in Kidneys provide large surface area for reabsorption to take place

• Depending on body’s needs, permeability of cells of the tubule can be altered (facultative reabsorption)

What is inside the proximal tubule?

• microvilli line proximal tubule and create bush border

• Greatly increases surface area for reabsorption

What is tubular secretion?

• tubular secretion adds materials from the blood to filtrate

Tubular secretion aims to:

• maintain blood pH (7.4-7.5) by removing excess hydrogen and ammonium ions

• Maintain ruin pH (6)

Active transport, through PCT and DCT

Reabsorption with structures and how they transport across

Structure	Substance	Active/passive
PCT	Water (60-70%) Salts (60-70%) Glucose (100%) Amino acids (100%) Vitamins (100%)	Passive (osmosis) All active
Loop of Henle	Water (25%) Na+/Cl- (25%)	Passive (osmosis) Active
DCT	Water (5%) Na+/Cl- (5%)	Passive (osmosis) Active
Collecting duct	Water (5%)	Passive (osmosis)

What is Urine?

• clear, transparent fluid. Normally amber colour

• Collected in bladder, eliminated through urethra

• Average amt of urine in 24 hrs os ~1,200 cm³

Where is Urine stored?

• Water and other substances not reabsorbed drain into collecting ducts, then renal pelvis

• Urine drains into ureters and is pushed y waves of muscle contractions

• Urethra carries urine from bladder to exterior of body

What is the Composition of Urine?

• varies according to diet/warter intake/ health

Typically:

• ~96% water

• ~4% other solutes, organic molecules, ions, and other metabolic wastes:

  • ~ 2% urea

  • Creatinine

  • Uric acid

  • Sodium, chloride, other irons (1,5%)

• Does not contain glucose or significant amt of protein

What is Uric acid created from?

• Uric acid created from metabolism of purines

• Purines come from the breakdown of Nucleic acids, when cells die, and also occur in many foods

What is creatinine created from?

• produced in muscle from the breakdown of creating phosphate. (Phosphatecreatine. An energy-rich molecule

What is delamination?

How does the liver play a role in the excretory system?

Ammonia into urea

Create bile for waste excretion

The liver processes and metabolizes various harmful substances

What is protein like in the excretory system and deamination?

• excess protein in diet cannot be stored in cells of the body

• Body needs to break it down to remove it

What happens to unused protein in deamination?

Protein can come from:

• worn out/broken cells, and broken down into amino acids to make new proteins

• Can be lost from body via urine, skin, hair and fingernails

• Protein helps form cell structures, enzymes, antibodies, and glandular secretions

How is Protein used for Energy?

• initially body uses carbohydrates and fats for energy

• When carbohydrates are depleted, fats in food and stored fats are used to release energy

• Protein NOT utilised in energy-releasing reactions, MAJORITY of the time

• To use Protein for energy, body can metabolise large amounts of protein

What is deamination?

• Deamination is the removal of the amino group from an amino acid molecule

• It occurs in the liver with the aid of enzymes

What is the equation for Deamination?

What do the two equations for deamination mean?

It shows how amino acid, turns into ammonia, and some energy, and from ammonia turn into urea, which can then be excreted in urine.

It shows how we can excrete excess waste and protein. ?

What is the purpose of deamination?

crucial process for:

• balancing protein metabolism

• ensuring the proper excretion of nitrogenous waste

• allowing body to utilize amino acids for energy

• other metabolic needs. 

What is ammonia? Ands it’s features

• soluble in water, highly toxic to cells

• Urea much safer for body

• Excreted by kidneys and eliminated from body in urine

• Also last in sweat

What is the whole structure of the Nephron’s (including capillaries)