Body Systems L3

• FLG211: BODY SYSTEMS
• DR ROSS ANDERSON
• DEPARTMENT OF PHYSIOLOGY
• WHAT WE ARE GOING TO COVER
• Topics to be covered

  • Various organ systems of the body
  • Function of the various body systems
• Body system


  A combination of tissues and organs that fulfill a specific function in the body
• Major organ systems


  • 11 (12 if you distinguish between male and female gonads)

  
• Integumentary system


  • Comprises the skin (integument), but also nails, hair etc
  • Has a physical barrier function, but is also contains sensory receptors, regulates body temperature and fluid loss
  • Vitamin D synthesis
• Epidermis


  • Stratified squamous epithelia
  • Regenerates from stem cells in the basal layer
  • No blood
  • Keratinocytes (produce keratin), melanocytes (produce melanin; MSH), Merkel cells (mechanoreceptors; touch), and Langerhans cells (macrophages)
  • Basal lamina – basement membrane that serves as an attachment point

  
• Dermis


  • Irregular and loose connective tissue (collagen and elastin)
  • Elastin and collagen provide skin with elasticity
  • Two dermis layers: reticular dermis at the bottom (blood vessels, glands, hair follicles, lymphatics and nerves, and fat; papillary dermis at the top (collagen, fibroblasts, capillary loops, nerve fibres, touch receptors (Meissner corpuscles))
  • Eccrine sweat glands and apocrine sweat glands (direct to skin, and onto hair follicle respectively). Temperature regulation
  • Sebaceous glands – associated with hair follicles. Secrete sebum (prevent drying out of skin)

  
• Hypodermis (subcutaneous)


  • Beneath the skin
  • Attached to dermis with collagen and elastin
  • Contains adipose tissue (fat cells)
  • Often inject here to reduce/slow absorption (fewer blood vessels)
• Skeletal system


  • Provides support, structure and protection
  • Bones, cartilage, joints, ligaments, tendons
  • Produces blood cells
  • Stores inorganic salts and calcium, for pH regulation
• Cortical bone


  Hard bone
• Cancellous bone


  Trabecular/spongy bone
• Cancellous bone


  • Has porous structure filled with red marrow
  • Red marrow is the site of blood synthesis (haematopoesis)
  • Yellow marrow has a much higher fat cell content and is primarily located in the central cavities of long bones
• Bone is primarily composed of calcium minerals (hydroxlapatite) and collagen
• Bone as a calcium reservoir

  • Large amounts of calcium stored in bone (99% of all calcium in the body)
  • Bone acts as a calcium store - breakdown of bone increases blood calcium, deposition of bone decreases blood calcium
• Osteoblasts


  Build bone (to store calcium)
• Osteoclasts


  Breakdown bone (to release calcium)
• Delicate balance between osteoblasts and osteoclasts, regulated by hormones
• Digestive system


  • Mouth, tongue, teeth, salivary glands, pharynx, esophagus, stomach, liver, gallbladder, pancreas, small and large intestines
  • Receives, breaks down, and absorbs food
  • Eliminates unabsorbed material from the body

  
• Gastro-intestinal tract


  The primary function is to move nutrients, water and electrolytes from the external environment into the body's internal environment
• GIT anatomy


  • Mouth
  • Esophagus
  • Stomach
  • Pyloric valve (gatekeeper)
  • Small intestine (most digestion/absorption) - duodenum, jejunum, ileum
  • Large intestine (solid fecal production)
  • Rectum
• Stomach


  • Parietal cells in the gastric glands secrete HCl into the stomach
  • Pyloric sphincter is responsible for controlling food entry into the duodenum
  • Mucous cells for protection of stomach (foveolar cells - produce mucins)

  
• Small intestine


  • Most nutrient absorption occurs
  • Digestive enzymes secreted by epithelial cells, hepatocytes and the pancreas aid in digestion, and create a soup called "chyme"
  • Goblet cells secrete protecting mucus
  • Brunner's glands secrete protecting mucus (duodenum)
  • Chyme contains water, ions, nutrients, and enzymes
  • Large surface area (villi and crypts) facilitate nutrient absorption

  
• Large intestine


  • Only approx. 1.5L enters large intestine/day
  • Cecum is a blind ending pouch – in herbivores it contains bacteria for breaking down cellulose, but in humans this function has been lost
  • Colon absorbs liquid from chyme to produce solid feces
  • Distention of the rectal wall initiates the defecation reflex, and a stool is passed
• Pancreas


  • Is a secretory gland (insulin, glucagon etc)
  • Secretes bicarbonate to neutralise stomach acid/chime
  • Secretes digestive enzymes (acinar cells) - Trypsin/chymotrypsin (proteins), Lipases (fats), Amylase (carbohydrates), Other hydrolases
  • Two ducts (main and accessory) enter the duodenum
• Gall bladder and liver

  • Liver cells (hepatocytes) secrete bile (stored in gall bladder)
  • Bile is not an enzyme, and instead acts like a detergent, in the emulsification of fats
  • Emulsification is the breakdown of fat into smaller fat droplets which the pancreatic lipases can then hydrolyse into fatty acids and glycerol
  • Bile is composed of bile salts (detergent-like), bilirubin (waste products of haemoglobin degradation), and cholesterol
• Nervous system


  • Nerves and sense organs, brain, and spinal cord
  • Receives stimuli from external and internal environment
  • Conducts impulses
  • Integrates activities of other systems
• Neuron


  Functional unit of the nervous system
• Types of neurons


  • Afferent (sensory) neurons – carry information from organs/tissues to the CNS
  • Efferent (motor) neurons – carry information from the CNS to target cells
  • Interneurons – connect afferent and efferent neurons within the CNS
• Neurons receive and pass on signals
• Nerves/nerve tracts


  • On their own, neuronal axons are quite vulnerable (very thin and sometimes have to traverse large distances)
  • Evolution has bundled these neuronal axons together to make them tougher (strength in numbers!)
  • In the PNS they are called nerves
  • In the CNS they are called nerve tracts
  • Sciatic nerve is the largest
• Cardiovascular system


  • Heart, blood vessels, blood, lymph and lymph structures
  • Moves blood through the vessels
  • Moves lymph through the lymph vessels
  • Carrier of gases and nutrients
  • Carrier of endocrine molecules
  • The heart pumps blood with a rhythm determined by a group of pacemaker cells (generate an electrical current that causes the heart muscles (myocardium) to contract)
  • Almost a third of all human deaths are due to cardiovascular disease
  • First heart transplant in South Africa (1967)
• Almost 100,000 km of vasculature in your body
• Endocrine system


  • Reproduction, stress, metabolism, growth, digestion etc
  • Secrete hormones into blood/general circulation
  • Differs from the exocrine system in which substances are secreted externally (into the lumen of the GIT for example)
• Hormones


  • Tyrosine and phenylalanine
  • Tryptophan
  • Polyunsaturated fatty acids (PUFA's)
• The nervous system and endocrine system are intimately linked
• Ways endocrine organs can be linked to the nervous system


  • Some neurons innervate endocrine organs directly
  • Neurohormones released by the brain
  • Can be activated by a direct stimulus (no nervous system input) - glucose/insulin, Ca2+/PTH
• Muscular system


  • Locomotion
  • Pumping blood
  • Movement of materials (myometrium, muscularis propria etc)
  • Body heat
  • Skeletal, smooth (non-striated) and cardiac muscles
  • Approx 600 muscles in the body