⭐ Excretion In Humans

✏ (Definition): Process by which metabolic waste products and toxic products are removed from the body of an organism

🖊 Done through (excretory organs)

(2) Kidneys

(3) Skin

(1) Lungs

(4) Liver

Carbon Dioxide

Excess mineral salts and nitrogenous waste products

Water

Excess mineral salts and nitrogenous waste products

Water

Excess bile pigments

✒ The Human Urinary System

(3) Urinary Bladder

(4) Urethra

(2) Ureter

(5) Sphincter Muscle

(1) Hilus

The renal artery, the renal vein and nerves are connected here


  • Urine from each kidney passes through the ureter to the urinary bladder
  • An elastic muscular bag located in front of the rectum
  • A narrow tube that connects the kidney to the urinary bladder
  • Stores urine
  • The duct through which urine passes from the bladder to outside of the body
  • Located at the bottom of the bladder
  • Used to control urination
  • When the bladder is full: sensory neurones send nerve impulses to the brain
  • To urinate: the brain sends nerve impulses to the sphincter muscle to cause it to relax. Urine is then able to flow into the urethra and out of the body

🚩 Kidney

Parts 85159919-anatomy-kidney-cross-section-showing-the-major-parts

(3) Renal Pyramid

(1) Cortext

(4) Renal Pelvis

  • Outer dark red region, covered and protected by a fibrous capsule

(2) Medulla

  • Renal pyramids are located here
  • Human kidney contains 12-16 renal pyramids
  • Numerous kidney tubules = nephrons (urine is formed here)
  • Enlarged portion of the ureter inside the kidney
  • Inner pale red region

Nephrons Figure_41_06_04

Parts of Nephrons

(5) Collecting Duct

(3) Loop of Henle

(2) Proximal Convulated Tubule

(1) Bowman's Capsule

(4) Distal Convulated Tubule

Pathway of Blood

(2) Each arteriole further branches into a mass of blood capillaries (glomerulus), glomerulus + bowman's capsule = Renal Corpuscle

(3) Blood then enters blood capillaries surrounding the nephron

(1) Blood enters the kidney by the renal artery, which branches into arterioles

(4) Blood capillaries then unite to form venules, which in turn forms a branch or the renal vein

🏴 Urine Formation

Ultrafiltration

Selective Absorption

Caused by high hydrostatic blood pressure:

  • The afferent arteriole that brings blood into the gomerulus is wider than the efferent arteriole that brings blood away
  • Creates high blood pressure into the glomerulus = provides main force reuqired for filtration process
    ∴ Forces water and small molecules out of the glomerulus and into the Bowman's Capsule

Partially permeable membrane

  • Wraps around the blood capillaries, like a very fine filter
  • Basement membrane = has very small pores, allows only water and very small molecules to pass through

Loop of Henle

Distal Convulated Tube

At the Proximal Convulated Tube

Collecting Duct

  • Glucose and Amino Acids reabsorbed (diffusion and active transport)
  • Most water reabsorbed (osmosis)
  • Some water reabsorbed
  • Some water reabsorbed
  • Mineral salts reabsorbed
  • Excess water reaborbed
  • Excess salts and metabolic waste products reabsorbed (as urine to renal pelvis)

Kidney Failure

🌸 Osmoregulation

The control of water and solute concentrations (levels) in the blood to maintain a constant water potential n the body

Depends on the amount of water and mineral salts

Controlled by aintiduretic hormone (ADH), produced by hypothalamus, released by the pituitary gland

(Loss of water)

  1. Water potential in blood plasma decreases
    1. Stimulates hypothalamus in brain
    2. Pittuitary gland releases more ADH to bloodstream
    3. Cells in the walls of collecting ducts more permeable to water, more water reabsorbed
      ∴ Smaller volume or urine produced, urine is more concentrated

(Large intake of water)

  1. Water potential in blood plasma increases
  2. Stimulates hypothalamus in brain
  3. Pituitary glands releases less ADH to the bloodstream
  4. Cells in the walls of collecting ducts less permeable to water, less water absorbed
    ∴ Larger volume of urine produced, urine is less** concenrated

Caused mostly by

Alcohol abuse

Severe accidents that physically damage the kidney

Diabetes

Complications from undergoing major surgery

High blood pressure

Treated through

Kidney Transplant

Dialysis Machine

Features of a dialysis machine

How does it work?

  1. Blood drawn from patient and is pumped through the machine
  1. Small molecules (urea, other metabolic waste products) diffuse out the tubing (partially permeable) into dialysis fluid
    Blood cells, platelets and large molecules remain in tubing

The dialysis fluid does not contain metabolic waste products

  • Sets up concentration gradient = waste products are removed from the blood

The tubing in the machine is narrow, coiled and long

  • Increases surface area to volume ratio = speeds up rate pf exchange of substances

Dialysis fluid contains the same concentration of essential substances as healthy food

  • Ensures that essential substances do not diffuse out, if blood plasma lacks these substances, substances can diffuse into the blood from the fluid,

The direction of the blood flow is opposite to the flow of the dialysis fluid

  • Maintains concentration gradient for the removal of waste products