Human Biology

• Vesicle


  Small membrane bound sac that transports materials into, out of, or within the cell
• Cell membrane


  • Outer boundary of the cell that separates neighbouring cells from external environment
  • Determines which substances gets into or out of the cell
• Golgi Body


  • Flattened membranes stacked on top of each other
  • Modifies proteins and packages them for secretion from the cell
  • Vesicles are pinched off the edges of the membrane
• Mitochondria


  • Sausage shaped like structure spread throughout the cytoplasm
  • Double membrane- outer; smooth and inner one is folded towards the centre of the mitochondrion
  • Releases energy for the cell through respiration
• Nucleus


  • Usually spherical
  • Contain genetic material (mostly DNA)
  • Double membrane that has gaps, nuclear pores through which large molecules can pass
• Nucleoles


  • Made of RNA
  • DNA & Nucleoles are surrounded in jelly-like nucleoplasm
• Lysosomes


  • Small spheres that contain enzymes to break down lipids, nucleic acids, proteins and carbs.
  • Breaks down materials take into or out of cell and break down organelles
• Cytoskeleton


  • Consists of microfilaments and microtubules that gives the cell its shape and assists its movement of materials, organelles or the whole cell
• Ribosomes


  Small amino acids are joined together at the ribosomes to make proteins
• Endoplasmic Reticulum


  • Pair of parallel membranes that connect the cell membrane to the nuclear membrane
  • A surface where chemical reactions can occur
  • The channels between the paired membranes are used for storage or transport of materials
• Centrioles


  • Small cylindrical structures located near nucleus involved in reproduction of the cell
• Cytoplasm


  • Thick fluid within cell membrane
  • Jelly-like or water material that fills all the space between nucleus and cell membrane
  • Made up of cytosol and organelles
• Cytosol

  • Controls osmotic pressure of the cell
  • 75-90% of water
• Function of the urinary system

  • To rid the body of wastes, especially nitrogenous wastes such as urea
  • To regulate the balance of fluid, salt and pH
• How the urinary system achieves its functions

  Filtering the blood as it passes through the kidneys
• Components of the Urinary System

  • Kidneys x2
  • Urinary bladder x1
  • Ureters x2
  • Urethra x1
• Blood Supply to Kidneys

  • Oxygenated blood in
  • Abdominal aorta feeds blood to the left and right renal artery
  • Deoxygenated blood out
  • The left and right renal vein feed blood to the inferior vena cava
  • Receives ~ quarter of the blood from the left side of the heart
  • Approx. 1.2 L of blood pass through the two kidneys every minute
• Renal Capsule


  A thin membrane that covers the outer surface of each kidney, providing support and protection to the kidney tissue
• Nephron


  • A structure within the renal pyramid
• Urine Formation Process

  1. Glomerular Filtration

  2. Reabsorption

  3. Tubular Secretion
• Blood Supply to the Nephron

  1. The renal artery supplies blood to the afferent arteriole to the glomerulus

  2. The blood is filtered there

  3. The efferent arteriole leaves the glomerulus

  4. The afferent arteriole has a wider diameter than the efferent arteriole

  5. This increases resistance to the flow of blood and produces a higher pressure in the glomerulus
• Glomerular Filtration

  • Blood is filtered to create a fluid called filtrate which occurs in the renal corpuscle, enhanced by blood pressure
• Deamination

  1. Removal of an amino group (NH2) from an amino acid

  2. Occurs in liver with help of enzymes

  3. Remaining product converted into ammonia (NH3) and carbohydrate
• Glomerular Filtration

  1. Blood enters the glomerulus

  2. High pressure forces water and dissolved blood components through the glomerular capsule
• Carbohydrate component

  Used to generate ATP
• Glomerular Filtration

  • Difference in pressure between the capillaries and tissues
• Ammonia

  Very toxic and soluble in water, so it must be converted to a less toxic form - Urea
• Glomerulus

  • Network of capillaries
  • One cell thick wall
  • Differently permeable membrane, selective in what it allows in and out
• Glomerular Capsule

  • Collects filtrate from glomerulus
  • One cell thick wall
• Conversion of ammonia to urea

  Urea then circulates the body and is removed by the kidneys and eliminated in urine
• Other functions of the liver

  • Detoxifies alcohol and many other drugs
  • Deactivates many hormones
  • Breaks down haemoglobin from dead red blood cells to produce bile pigments which are passed out of the body with faeces
• Glomerular Capsule

  • Performs the first step in the filtration of blood to form urine
  • Holds the glomerulus which supplies blood for the kidney to filter
• Functions of skin

  • Physical barrier protecting from external environment
  • Role in excretion
• Glomerular Capsule

  • Lining the capsule are specialised cells called podocytes
  • These cells have finger-like extensions that wrap around the capillaries of the glomerulus
  • The spaces between the "fingers" are filtration slits
  • Play an active role in preventing plasma proteins from entering the filtrate
• Skin's role in excretion

  1. Sweat glands located in the lower layer of the skin and a duct transports the sweat

  2. Even with no visible perspiration, the sweat glands secrete about 500mls of water a day

  3. Dissolved in the water are salts, lactic acid and urea
• Renal Tubule

  • Long and convoluted structure from the glomerulus
  • Divided into 3 parts: Proximal convoluted tubule, Loop of Henle, Distal convoluted tubule
• Proximal convoluted tubule

  • Due to its proximity to the glomerulus
  • It stays in the renal cortex
  • Maximum reabsorption
  • Lined with simple cuboidal epithelium
• Proximal convoluted tubule


  • Function: To reabsorb essential substances such as glucose, proteins, amino acids
  • Structure: Microvilli line the proximal tubule and create a brush border, which greatly increases the surface area for reabsorption
• Loop of Henle

  • A loop (with descending and ascending limbs) that goes through the renal medulla
  • Descending limb= permeable to water, impermeable to electrolyte
  • Ascending limb= permeable to electrolytes but impermeable to water
• Loop of Henle

  Since the electrolytes get reabsorbed at the ascending loop of Henle, the filtrate gets diluted as it moves towards the ascending limb. But reabsorption is limited in this segment.