Excretion

Waste products of plants

• Oxygen

• Carbon dioxide

• Water/water vapour

Excretion

The removal of waste substances of metabollic reactions

Metabolic waste produced by the human body

• Carbon dioxide and water

• Urea

• Substances in excess

Organs for excretion

• Kidneys- Urea

• Lungs- Carbon Dioxide

• Skin- Water, excess mineral ions, some urea (Sweating)

Functions of the kidney

• Regulate water content of the blood

• They excrete the toxic waste products of metabolism

Osmoregulation

The process of maintaining the water and salt concentrations

Importance of osmoregulation

• Maintaining water levels

  • Too much water- Cells swell up and can burst

  • To little water- Cells loose water and can die

Key features of the urinary system

• To filter waste products from the blood and expel it from the body as urine

• To control water levels of the body

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Kidney

• Filters the blood

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Ureter

• Tube connecting the kidney and the bladder

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Bladder

• Organ that stores urine as it is produced by the kidney

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Urethra

• Tube that connects the bladder to the exterior, where urine is released

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Renal artery

Comes from the aorta delivers oxygenated blood to the kidney

3 main sections of the kidney

• Cortex

• Medula

• Renal Pelvis

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Proximal convoluted tubule

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Glomerulus

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Bowman’s capsule

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Distal convoluted tubule

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Collecting duct

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Loop of henle

Ultrafiltration process

• Arterioles branch off the renal artery and lead to each nephron, forming a glomerulus inside the Bowman’s capsule.

• The capillaries narrow, increasing blood pressure and forcing small molecules out of the blood into the Bowman’s capsule, forming glomerular filtrate.

Components of glomerular filterate

• Urea

• Water

• Glucose

• Salts

Why can’t proteins and red blood cells be filtered during ultrafiltration

They are too large

Selective reabsorption

• Occurs in the nephron, primarily at the proximal convoluted tubule.

• Glucose, some salts, and most water are reabsorbed back into the blood.

• Active transport is used for glucose reabsorption, requiring mitochondria for energy.

How is water absorbed

Osmosis

How are salts absorbed

Active transport

Why do people with diabetes have glucose in their urine

Their blood glucose levels are too high for complete reabsorption.

Adaptation of the nephron

Contains a lot of mitochondria which provides energy for active transport of glucose molecules

Role of ADH

• Controls water reabsorption

• Affects the permeability of the collecting duct

• Maintains water levels by negative feedback

Gland that releases ADH

Pituitary gland in the hypothalamus

High water content

• The hypothalamus detects high water levels

• Less ADH is released → Collecting duct is less permeable

• Less water is reabsorbed

• Large volume of dilute urine

Low water content

• Hypothalamus detects low water content

• More ADH is released → collecting duct is more permeable

• More water is reabsorbed

• Small volume of concentrated urine

Composition of urine

• Excess water

• Excess mineral ions

• Urea

Factors affecting urine

• Exercise

• Water intake

• Temperature

Effect of high water intake on urine

• More water removed

• Large volume of dilute, pale urine.

Effect on low water intake on urine

• Less water removed

• Small volume of concentrated, dark urine

Effect of high temperature on urine

• More water lost in sweat

• Less water in urine

• Small volume of concentrated, dark urine

Effect of exercise on urine

• More water lost in sweat

• Less water in urine

• Small volume of concentrated, dark urine