Excretion, ch.31

• The Nephron

  • is the functional unit of the kidney, as they make urine.
  • The main process is (filtration, reabsorption, secretion)
  • they are located in the medulla and cortex of the kidney.

  
• Blood Supply to the Nephron

  • Blood enters the kidney through the Renal Artery, forming many renal arterioles which then divide and form smaller afferent arterioles.
  • These afferent arterioles divide and form a cluster of capillaries called the glomerulus in the Bowman's capsule.
  • The blood leaves the glomerulus through the efferent arteriole
  • The efferent arteriole divide and the capillaries surround the rest of the nephron
  • These capillaries eventually rejoin and make renal venules, eventually leaving the kidney as the renal vein.
• Filtration in Nephron

  Filtration occurs in the glomerulus.

  1. blood entering the nephron through the afferent arteriole contains waste products.
  2. small molecules get forced out of the plasma, through the glomerulus into the Bowman's capsule. This forms a dilute solution called the glomerular filtrate.
  3. Large globular proteins cannot get filtered through and do not enter the glomerular filtrate. e.g. red and white blood cells, antibodies, hormones.
• Reabsorption

  Proximal Convoluted Tubule

  1. the proximal tubule reabsorbs most of the water by osmosis.
  2. It reabsorbs useful substances e.g. glucose, amino acids, vitamins through a combination of active transport and diffusion.
  3. The structure of the proximal tubule is aided with:

  • has many infoldings for large surface area
  • is one cell thick
  • has many mitochondria to provide energy for active transport.
• Reabsortion

  Loop of Henle

  • the descending loop of Henle is permeable to water and reabsorbs a small amount of water through osmosis.
  • The ascending loop of Henle is permeable to salts and salts move by diffusion. At the top of the ascending limb, sodium is pumped out by active transport.
  • This addition of salt in the medulla increases solute concentration making it more concentrated than the fluid in the tubule.
  • Therefore due to osmosis, water is forced out of the neighbouring descending loop of henle and the collecting ducts. Function of the Loop of Henle is to reabsorb water.
• Reabsorption

  Collecting ducts

  The collecting duct is permeable to water. A small amount of water is reabsorbed from the filtrate through osmosis because of salt concentration in the medulla.
• Secretion

  Secretion is when some substances are passed from the blood to the nephron.

  The distal tubule has the precise control of water, salt and pH values in the blood.

  E.g. potassium and Hydrogen Ions. They are harmful in the blood (potassium affects nerve impulses) (hydrogen ions affect pH)

  therefore kidneys also control blood pH.

  Purified blood leave through the renal vein.
• The bladder stores urine
• The glomerular Filtrate compared to Urine

  • glomerular filtrate contains more water (more dilute) than urine
  • The glomerular filtrate contains useful substances not found in urine e.g. vitamins
• ADH - anti-diuretic hormone
• The Volume of urine is controlled by the hormone ADH. It is:

  • produced in the hypothalamus, and stored and released by the pituitary gland
  • it is released from the pituitary gland into the bloodstream
  • The bloodstream carries it to the kidney where it affects the distal tubule and the collecting ducts.
  • These become more permeable allowing more water to be reabsorbed into the blood from the nephron
• Blood plasma becomes too concentrated when we:

  • don't drink enough water
  • lose too much water with sweat or faeces
  • consume too much salt
• Excretion is the removal of metabolic waste from the body
• Plant waste products are stored in vacuoles

  • plants lose oxygen and water
  • lost through the stomata on leaf and lenticels on stem
• Homeostasis

  The need to control body temperature is because temperature affects the rate of chemical reactions. High temperatures can denature enzymes, while cold temperatures can slow down reactions.
• Ectotherms - lose or gain heat to or from their external environments. e.g. lizards, snakes

  Endotherms - generate their own heat in their body from metabolic reactions
• • The epidermis is the outer layer of the skin, it acts as a sealed barrier to prevent water loss and the entry of pathogens.
  • cells in the malphigian layer divide by mitosis to form new epidermal cells. As these cells go through the granular layer, they form a waterproof keratin. As this keratin builds up a more cornified layer is formed.
  • Due to too much keratin buildup or lack of blood capillaries, the cornified layer cells die.
• Specialised cells in the malphigian layer produce a brown/black pigment called melanin that protects the skin from UV rays. The production of melanin increases as exposure to sunlight increases.
• The dermis is the inner layer, consists of connective tissues and produces a strengthening protein called collagen.
• Functions of the Skin

  1. Protection
  2. Vitamin D production
  3. Food Store
  4. Sensing
  5. Excretion
• 1. Protection

  • The epidermis acts as a sealed barrier protecting from the loss of water and entry of pathogens
  • the dermis prevents damage to internal organs
  • the malphigian layer produces melanin that protects the skin from UV rays
  • The sebaceous gland releases sebum which is an anti-bacterial oil.
• Sebum keeps the hair moist and flexible and prevents the skin from drying
• 2. Vitamin production

  • Vitamin D is produced following exposure to UV rays, this helps absorb calcium
• 3. Food storage

  The adipose tissue stores food
• 4. Sensing

  there are a variety of sense receptors that allow for the ability to sense things like touch, pain or temperature
• 5. Excretion

  The skin excretes salt and water. Sweat glands excrete this when sweating.
• Temperature regulation

  -- Cold conditions

  • blood vessels contract from the surface of the skin in a process called vasoconstriction, which retains heat and reduces heat loss
  • erector muscles contract forming goosebumps and the hairs to stand up straight. This traps a layer of warm air very close to the surface of the skin, reducing heat loss. This is called piloerection
  • the brain detects low blood temperature and the hormone adrenaline causes the muscles in the body to contract and relax rapidly (shivering)
  • fat in Adipose tissue insulates the body
• Temperature Regulation

  -- Warm conditions

  • blood vessels expand and go to the surface of the skin, radiating heat, and reducing body temperature
  • Sweat glands release sweat which cools you when it evaporates
• Organs of Excretion

  Lungs - excrete water & carbon dioxide

  Skin - excretes water & salt

  Kidney - excretes water, salts & urea
• Kidneys are located just below the diaphragm and in the small of the back
• Functions of the Kidney

  Excretion - remove waste products from the blood and convert them into urine

  Osmoregulation - water content- Controls water content in the body by varying water content in urine.

  salt content - controls salt content in the body by varying salt released in urine.

  Kidneys ensure that blood plasma has the same concentration as normal body cells. Kidneys are said to be osmoregulatory.

  Kidneys also ensure the pH of the blood remains at 7.4
• Urine

  Urine is composed of

  • water - 96%
  • Nitrogenous Waste - 2.5%
  • Salts - 1.5%

  Urine flows from the medulla region into the renal pelvis. The waste is then carried by two ureters.