chapter 11 - homeostasis

• functional unit of kidney

  • nephron
  • 1 million per kidney
• structure of kidney divided into 2 parts

  • cortex
  • medulla
• what is the deepest layer of the kidney?

  renal pelvis
• kidney has a special type of system?

  portal system - 2 sets of capillaries in a series through which blood must travel before reaching the heart
• blood flow in the kidney

  • blood enters through the renal artery
  • branches into smaller blood vessels called arterioles
  • arterioles carry blood to a network called glomeruli
• second set of capillaries

  • vasa recta helps further filter and reabsorb substances from the blood
• glomerulus

  kidney's filtration system

  surrounded by a cuplike structure called bowman's capsule
• bowman's capsule

  • collects filtered fluid from the blood and leads to different places via the tubules
• tubules of the bowman's capsule

  1. proximal convoluted tubule
  2. descending limb of loop of henle
  3. ascending limb of loop of henle
  4. distal convuluted tubule
  5. collecting duct
• osmoregulation

  3 steps
• osmoregulation step 1 - filtration

  • occurs in the glomerulus
  • small molecules like glucose enter
  • large molecules like proteins and blood cells cannot
  • kidney filters 180 liters of blood a day
• osmoregulation step 2 - secretion

  • nephrons actively/passively transport salts, acids, bases, and urea directly into the tubules
  • kidneys can also remove extra ions/substances from blood when there are too many of them
  • also gets rid of waste that is too large to pass through tiny pores of the glomerulus
• osmoregulation step 3 - reabsorption

  • kidneys retrieve useful substances that have been filtered/secreted into the tubule
  • make sure body retains necessary nutrients and maintains balance
• proximal/distal tubes

  • reabsorb water

  loop of henle

  • descending limb - water in, no salt
  • ascending limb - salt in, no water

  collecting duct

  • reabsorbs water depending on the body's needs
• osmolarity gradient

  • concentration of solutes (like salts) in a solution
  • crucial for regulating water balance in body
  • concentration of solutes in kidney tissue changes from outer (cortex) to inner part (medulla)
  • cortex - concentration is similar to that of blood
  • medulla - concentration can be much higher
• hormonal regulation - antidiuretic hormone (ADH)

  • also known as vasopressin
  • makes collecting duct more permeable to water
  • more water is reabsorbed from the filtrate and back into the bloodstream
  • helps retain urine, especially when dehydrated
• hormonal regulation - aldosterone

  • increases reabsorption of sodium in collecting duct
  • indirectly increases water reabsorption because water follows sodium
• excretion - final step where waste leaves the body

  point of no return

  • in collecting duct
  • anything remaining in the tubule is excreted
  • no more reabsorption

  flow of waste

  • filtrate (urine) collects in the renal pelvis
  • renal pelvis ---> ureter (through bladder) --->urethra

  healthy urine - no blood, protein, or glucose
• liver digestion

  digestion

  • produces bile to break down fats for reabsorption blood glucose regulation

  blood glucose regulation

  • after eating - stores extra glucose converting it into glycogen
  • when hungry - coverts glycogen back into glucose and release into bloodstream

  nitrogen waste management

  • breaks down amino acids when there is not enough glucose
  • converts ammonia into urea, then excreted by the kidneys
• the skin

  • the largest organ in the body - 16% of total body weight
• epidermis

  • outermost layer
  • 5 sub layers inwards
  • deepest layer - stratum basalis ---> cells push up towards surface
  • as reach outer layer ---> cells die and form a tough protective barrier
• dermis

  • middle layer - 2 parts
  • papillary layer - upper part w/ loose connective tissue
  • reticular layer - lower part w/ denser connective tissue
• hypodermis (subcutaneous layer)

  • deepest layer
  • made of connective tissue that attaches skin to body