integument physiology Flashcards
functions of the integument
- Protection e.g.
* Physical (e.g.fat, collagen, keratin).
* Radiation (e.g.melanocytes).
* Epidermal organs (horns, claws). - Immune defence e.g.
* Physical barrier to infection
* Immune cells in skin
* Antimicrobial properties in skin gland secretions. - Sensing environment e.g.
* Pressure receptors.
* Stretch receptors.
* Pain receptors.
* Heat receptors.
* Cold receptors.
* Tactile hairs. - Thermoregulation e.g.
* Sweating.
* Hairs, piloerection and arrector pili.
* Blood flow to skin.
* Insulation by fat. - Storage and excretion e.g.
* Fat stores energy, water and vitamins.
* Glands can excrete water and electrolytes.
skin sensors
» Mechanoreceptors.
* Ruffini’s end organ or bulbous corpuscle – skin
stretch.
* Krause end bulb or bulboid corpuscle–cold.
* Meissner’s corpuscle or tactile corpuscle – change in texture, slow vibrations.
* Pacinian corpuscle or lamellar corpuscle – pressure, fast vibrations.
* Merkel’s disc, a free nerve ending with discoid terminals – sustained touch and pressure.
» Nociceptors.
* Free nerve endings can act as nociceptors –
pain.
» Thermoreceptors.
* Free nerve endings can act as thermoreceptors for hot or cold.
water homeostasis
» Water input:
* Free water intake (drinking)
* Water in food.
* Metabolic water.
» Water output:
* Urine.
* Faeces.
* Insensible losses – evaporation from skin and airway.
electrolyte homeostasis
-electrolytes are minerals in blood and other bodily fluids that carry an electrical charge
-help maintain blood chemistry (eg acidity) and muscle action
-electrolytes are lost in sweat and replaced by drinking water with electrolytes
-maintained by osmoreceptors in the hypothalamus
acid- base homeostasis
-balance between H+ (pH)
-essential for enzyme function
what controls homeostasis
hypothalamus region of the brain
hypothalamus
» Coordinates activities of autonomic nervous system (ANS).
* Sympathetic (fight or flight).
* Parasympathetic (rest and digest).
* Enteric nervous system.
» Controls a major part of the endocrine system.
» Detects the osmolarity of the interstitial fluid in the brain via osmoreceptors.
» Monitors brain temperature.
how is thermoregulation controlled
-the hypothalamus receives nerve impulses from cold and warmth thermoreceptors (free nerve endings) within the skin
-Also thermosensors within hypothalamus itself and within spinal cord, visceral organs and nasal/oral cavities
importance of thermoregulation
-enzymes only work at optimum temperature
-below 34 degrees animals can’t regulate their own temperature
-27-29 means cardiac fibrillation and death
-45 can mean fatal brain lesions
hypothermia
below normal body temp (heat loss exceeded production)
hyperthermia
-above normal body temperature
fever
reset of hypothalamic set point to higher temperature
thermoregulation negative feedback
» Hypothalamus has heat loss centre (detects higher than set point so starts process of heat loss).
» When temperature corrected heat loss centre switches off.
» Hypothalamus has heat conservation centre (detects lower than set point so starts process of conserving/generating heat).
» When temperature corrected heat conservation centre switches off
how do animals produce heat
-by-product of all metabolic processes
-exercise (work done converted to heat energy)
-eating (supply of energy)
-muscle contraction (shivering thermogenesis)
-brown adipose tissue (non-shivering thermogenesis)
-fever
non-shivering thermogenesis
» Increased heat production via increased metabolism.
» In response to chronic cold external factors
» Mediated via:
* Increased thyroxine secretion (hormone from thyroid gland).
* Increased sympathetic (ANS) activity (norepinephrine).
* Increased metabolism of lipids in response to circulating catecholamines (norepinephrine/epinephrine).
» Brown adipose tissue.
brown adipose tissue
-prodominantly in neonates as they have a larger body surface to volume ratio
-darker colour as high density of mitochondria with cytochrome (iron-containing) pigment
-smaller, numerous lipid droplets
where is brown adipose tissue located
-subcutaneous region between scapulae and around kidneys and myocardium
-presence of lipid in close proximity to many mitochondria facilitates rapid transfer of stored energy into heat
-stimulated by circulating catecholamines and norepinephrine secreted from sympathetic nerve endings
how do aniamls loose heat
» Radiation.
* When body warmer than environment lose heat by emission of infra-red radiation.
» Conduction and Convection.
* Directly from body surface to cooler objects in contact with the animal
* Transfer of heat by warm air to cooler air.
» Evaporation.
* Only form of heat loss when ambient temperature equals or is
greater than body temperature.
* Evaporation of 1L of water requires 2.43 kJ.
* Panting.
* Sweating.
panting
» Number of patterns act to increase heat loss through evaporation.
* Inhalation and exhalation through the nose.
* Inhalation through the nose and exhalation
through nose and mouth.
* Inhalation through the nose and mouth and exhalation through the nose and mouth.
» Vascular engorgement of respiratory and oral mucosa – especially turbinates.
» Increased salivation.
» (No gas exchange – dead space breathing)
sweating
» Poorly developed in dogs and pigs so of little use in
thermoregulation.
» Important means of thermoregulation in horses and cattle (from
apocrine sweat glands).
» Important means of thermoregulation in primates including humans (from eccrine sweat glands).
» Sheep sweat – but less useful under the wool!
» Cats can sweat but glands confined to paws, lips, chin and perineum
blood supply to the skin
-cutaneous arteries
-three plexus (deep or subcutaneous plexus, middle plexus, superficial plexus)
heat transfer within the body
» Tissue is a poor conductor of heat.
» Heat transported by the blood.
» Heat produced primarily in muscles and the liver.
» Heat lost through skin and respiratory tract as very good blood supply with many small vessel close to the body surface.
» Rise in core body temperature increases blood flow to the skin.
» Drop in core body temperature decreases flow and fur or plumage are raised (piloerection/goose bumps) to trap more air as insulation.
» Sympathetic nervous system regulates blood flow and piloerection
counter current exchange
» When trying to cool – peripheral vessels dilate and transfer heat to environment
» When trying to conserve heat – peripheral vessels constrict so blood shunted to deeper veins.
» Deep veins run close to artery carrying warm blood.
» Colder venous blood from extremities is warmed by exchange of heat from counter current of warm blood in the artery.
counter current in artiodactls
-carotid rete
» During selective brain cooling, cool venous blood from the nasal mucosa drains into the cavernous sinus via the angularis oculi vein (as well as some deeper veins).
» Can be bypassed in periods of high sympathetic activity
