Physiology two Flashcards

Question

Describe the synthesis of thyroid hormones ?

Answer 1

Thyroid hormone sysnthesis Iodine and tyrosine is required for thyroid hormone synthesis * stored extracellular in colloid of follicles * all aspects of thyroid hormone synthesis and secretion enhanced by TSH from the anterior pituitary * lack of iodine in inland areas restricts animals growth

Answer 2

Thyroid hormone transport * 93% of released hormone from gland is T4 * 7% is T3 * Over 99% of thyroid hormones are bound with plasma proteins * the thyroid hormones are released to tissues slowly by the plasma proteins * slow onset; long duration of action * affects all almost all tissues of the body * T3 in free form is the active hormone within the body * most T4 is converted to T3 in peripheral tissues via deiodination.

Answer 3

Mechanism of action of the thyroid gland * activates nuclear transcription of a large number of genes resulting in the synthesis of many proteins * increase in number of protein enzymes, structural proteins, transport proteins, and other substances are synthesised in virtually all cells of the body * increase in functional activity throughout the body

Answer 4

Thyroid hormone actions * increase cellular metabolic activity - increases 02 consumption * calorigenic effect produces heat * sets bodys basal metabolic rate BMR (may increase 60-100%) * mainatins level of metabolism for normal function Effect * increases number and activity of mitochondria * increase Na+K+ pump * permissive action on catecholamines (increase of cardiac output) * rate of utilization of food is increased * generally elevated in endoderms

Answer 5

Thyroid hormone effect on growth * essential for normal growth stimulates GH secretion * nessary for normal gonadal functions * frogs=metamorphosis Thyroid hormone effects on the central nervous system * Crucial role in the devlopment of CNS during foetal development + after birth, hatch * Essential for normal CNS activity in adult animals *

Answer 6

Regulation of thyroid hormone secretion Under control of the hypothalamic pituitary thyroid axis * TRH thyrotropin releasing hormone hypothalamus * acts upon the anterior pituitary which sectrets TSH to increase secretion of T3 and T4 * T3 and T4 provide negative feedback on the secretion of TSH and TRH Cold = enhances secretion highly adaptive in newborn animals Starvation = reduces secretion

Answer 7

Abnormal thyroid function Normal thyroid function = euthyroidism **Hyperactive thyroid gland** * elevated BMR * poor heat tolerance, increased appetite, increased HR * excessive mental alertness * frequently observed in older cats dur to adenomas benign tumors **Hypoactive thyroid gland** * frequently caused by thyroiditis, increased TSH and desensitization * low BMR, sluggish, low heart rate, dull mentation * poor tolerance to cold * weight gain * patchy fur * reduced apetite

Answer 8

Adrenal glands ## Footnote Comprised of a central medulla (nervous tissue), and outer cortex in most mammals Located on the top of the kidney

Answer 9

Adrenal medulla ## Footnote **Stimulus** Sympathetic nervous system stimulation, fight or flight response, hypoglycaemia, decrease in BP or cold exposure **Target** Heart, smooth, muscle, pancreas and eye **Secretion** Catecholamines = adrenaline / epinephrine (90%) and noradrenaline / norepinephrine

Answer 10

The effects of the adrenal medulla Short term stress response. * effects are carried out via alpha and beta receptors * incresaed cardiac output * arteriole constriction * increase in blood sugar levels * increase plasma fatty acids * dilation of pupil * combat short term acute stress Pheochromocytoma = Is a tumur of the adrenal gland causing excessive secretion of catacholamines

Answer 11

Adrenal cortex Essential for life - secrete steroid hormones (have lipid droplets contain cholesterol) Adrenocortical hormones mostly transported in bound form and act upon intracellular receptors **Zona Glomerulosa -** mineralocorticoids **Zona Fasciculata -** glucocorticoids **Zona reticularis -** sex steroids (source of sex hormones in castrated animals)

Answer 12

Adrenal glucocorticoids * secreted from fasiculata of the adrenal cortex * main glucocorticoid in mammals is cortisol * incresaes blood glucose (increase gluconeogensis) * enhances protein catabolism * permissive action to catacholamines and glucagon * anti inflammatory and immunosuppressive effects * may be used to suppress inflammatory reactions or allergic reactions Helps to adapt an animal to long term stressors ( such as herd seperation).

Answer 13

Glucocorticoid regulation * Regulated by the hypothalamo pituitary adrenal axis * influenced by stress and circadian rythm * indiurnal animals highest in the morning and lowest over night - the reverse is true in nocturnal animal * coricotropin releasing hormone * ACTH adrenocorticotrophic hormone Stress causes the release of cortisol - its release is proportional to the stressor

Answer 14

Mineralocorticoids Secreted from the Zona Glomerulosa within the adrenal cortex * aldosterone is the main mineralocorticoid * affect on Na+, K+ and Cl- * regulation or stimulus is via angiotensin 2 and elevated ECF Actions * Act upon the renal tubules * stimulation of Na+ reasorption * regulation of ECF volume * regulation of blood pressure * K+ level maintenance in ECF

Answer 15

All are disorders of the adrenal cortex **Cushing disease** * over secretion of CRH/ACTH (excessive cortisol) * common in older dogs * excess plasma glucose, protein shortage and fat deposition in abdomen **Addison's disease** * adrenocortical insuuficiency * certain dog breeds - life threatening **Conn's syndrome** * hypersecretion of aldosterone * tumor or adrenal hyperplasia

Answer 16

The pancreas The pancreas lies dorsally to the stomach in vertebrate, where it has both an exocrine and endocrine function. **Islets of Langerhans** * endocrine tissue * alpha = glucagon * beta = insulin * delta = somatostatin * PP cells produce pancreatic polypeptide All are peptide hormones involved in the control of metabolism

Answer 17

Insulin Physiology * circulates in unbound form * half life 5-8 mins * anabolic hormone and the liver is the most important target organ Actions * stimulates glucose entry to cells * increases glycogen storage within muscle and adipose tissue **(Glut 4)** * inceases glycogen production and storage in the liver * promotes fat synthesis (glucose fatty acid synthesis in the liver) * promotes protein synthesis (increase amino acid uptake)

Answer 18

Regulation of insulin Rising blood glucose above nornal is a powerful stimulator of insulin **Other stimulating factors** * rise in blood amino acid level * rise in blood fatty acid level * vagus stimulation * Some GI hormones (gastrin, CCK, secretin) * hyperkalemia (high potassium)

Answer 19

Glucagon Secreted by alpha cells in the pancreas; polypeptide Actions * catabolism of nutrients (especially between meals) * increase in blood glucose levels * increase FFA blood glucose levels * promotes conversion of fatty acids to ketone bodies * increase liver gluconeogenesis * increase lipolysis Note. A decrease in glucagon enhances breakdown of live glycogen

Answer 20

Glucagon Secretion is enhanced by a decrease in blood glucose levels * exercise * starvation * sympathetic stimulation * glucagon levels vary among species (bird twice as high as mammals) * elevated levels of amino acids in blood plasma results in an increase in both insulin and glucagon secretion. This ensures there is enough glucose available to utilize the amino acids from a protein rich diet. This is especially important in dogs and cats consuming a diet naturally high in protein.

Answer 21

Transiently high blood glucose consequences * Glycosuria = glucose in urine * polyuria = frequent urination due to osmotic diuresis * polydipsia = excessive thirst Swelling of the lens of the eye due to high osmotic pressure can result in transient blindness

Answer 22

Consequences of chronically high blood glucose * chronic bladder infections (due to glycosuria) * oxidative damage of capillary walls * poor circulation in the back of the eye leading to blindness * poor circulation can result in thinning skin and hair and infection * formation of cateracts (glucose converted to sorbitol in the lens) * ketoacidosis * vomiting (an emergency situation)

Answer 23

Catecholamines * increase blood glucose level * increases hepatic glucose output * decreased peripheral utilisation of glucose * increases FFA level Helpful to combat stressful situations eg exercise

Answer 24

Diabetes Diabetes Mellitus * means sweet * lack of insulin or its function * can be associated with glucagon excess * accumulation of ketone bodies (acidosis) * cataract * increased appetite weight loss * lack of energy Diabetes Insipidis * means without sweet * lack of antidiuretic hormone (ADH, vasopressin)

Answer 25

Glucocorticoids * increases blood glucose level * protein catabolism and protein mobilisation Function to combat long term stress and starvation

Answer 26

Type 1 and 2 diabetes **Type one insulin dependant** * total lack of insulin * occurs in many species including cats and dogs * require exogenous insulin for survival * arises from autoimmune reaction destroying beta cells * propensity to develop ketosis **Type two diabetes not insulin dependant** * insulin secretion normal or increased but target cells do not respond * many factors can cause the disease including genetic, obesety and age * encourage exercise, low carbohydrate diet high in protein and fibre

Answer 27

Parathyroid gland Location * dogs and cats beside or within the thyroid gland * pigs cranial to the thyroid Secretion * secretes parathyroid hormone * acts to increase the plasma concentration of calcium and lower PO4-

Answer 28

Actions of parathyroid hormone * on kidney increases Ca2+ reabsorption * on bone stimulates Ca2+ pumping from bone and long term by dissolution of bone * on intestine indirectly by activating vitamin D3 to absorb Ca2+

Answer 29

Regulation of parathyroid hormone Primary signal for PTH is low Ca2+ levels in plasma parathyroid cells have calcium sensing receptors on their surface.

Answer 30

Calcitonin Calcitonin is produced by C cells in the thyroid gland of mammals * by ultimobranchial glands in birds Action * decrease Ca2+ level in plasma (weak effect) * by decreasing Ca2+ secretion from bone * increase Ca2+ secretion in urine * secretion of calcitonin is enhanced via a rise in plasma Ca2+

Answer 31

Stanniocalcin The most important hormone for Ca2+ regulation in fish * synthesised in Corporades of Stannius within the kidneys of fish * reduces calcium uptake in kidneys, intestine and gills

Answer 32

Vitamin D stimulated by sunlight * indoor, heavily furred animals may need vitamin D suuplementation Actions - by the active form of vitamin D * up intestinal absorption of Ca2+ * up intestinal Po43- absorption * increase bone mineralisation Vitamin deficiency in young animals causes rickets, and osteomalacia (soft bones) in older animals.

Answer 33

Parturient paresis Excessive demands for calcium (eggs, milk) * prevent by providing a low Ca2+ and high phosphorus diet to stimulate PTH secretion * high calcium diet around the time of partuition * hypocalcemia not enough Ca2+ in blood steam leads to tremors, unconsiousness, coma and even death.

Answer 34

Atrial naturietic peptide The heart hormone * stimulated by an increase in blood pressure and a increase in Na+ * acts upon the renal tubules, aldosterone and vascular smooth muscle Acts to increase Na+ secretion reducing blood pressure

Answer 35

**Structure of the eye - three layers** **Outer protective layer** * posterier sclera = white tough membranous maintains the shape of the eye * anterior cornea = transparent first refractive surface **Middle layer uvea** * Choroid = vascular, pigmented * Tapetum lucidum = light reflective material * Cilary body = muscular structure * Iris = pigmented has an opening pupil **Inner layer Retina**

Answer 36

**Eye cavities** **Anterior cavity** Filled with **aqueous humor** - a clear fluid which supplies nutrients to the cornea and the lens. * continuously secreted by the ciliary epitheliuminto the posterior chamber after which it enters the anterior chamber * maintains intraocular pressure * Glaucoma sustained increase in intraoccular pressure **Posterior cavity** Vitreous humor - gelatinous transparent fluid which acts to maintain the shape of the eye ball

Answer 37

Functions **The aim is for the lens and cornea to focus immages onto the retina** Iris = regulates the amount of light entering the eye, has a dilating/constricting muscle Lens = Suspended by suspensory ligaments and attched to ciliary body. Flexible, biconvex focusses light rays to form an image on the retina * variable focussing power Fovea = in primates acts to minimize distortion of light and has the highest visual acuity. Tapetum = in most nocturanl and domestic animals, choroid has a patch of reflective material which reflects light and helps to improve vision in low light.

Answer 38

Nictitating membranes * all domesticated animals have athird eye lid nictitating membrane * provides extra protection from injury * retractor muscle contraction pulls the eyelid into the orbital, where the nictating membrane covers the front of the eye to varying degress * birds have a nictating membrane but no retractor muscle

Answer 39

Retina * histologically seperated into 10 layers * include five types of neyrons ganglion cells, bipolar cells, horizontal cells, amacrine cells, photoreceptors (rods + cones) * retinal detachment occurs frequently - serious complication When photons of light hit the photoreceptors it alters their membrane potential leading to the stimulation of ganglion cells.

Answer 40

Rods and cones - photoreceptors Outer segment contains a visual pigment - **opsin** Rods * rhodopsin * visual pigment helps with night vision * sensitive to light, low acuity, can not discriminante colours * mostly located in the peripheral retina Cones * visual pigment may have different opsins depending upon species * discriminate different colours * requires a higher level of illumination * better visual acuity, day time vision * concentrated mostly in the fovea region

Answer 41

Phototransduction * when the visual pigment is exposed to light it decomposes to form opsin and all trans retinal * metarhodopsin 2 generates a nerve action potential Role of vitamin A = (old hay horses) reduced vitamin A causes night blindness

Answer 42

Photopigments Cone system help for color vision by having different photopigments, each photopigment responds to a different wavelength of light * ratio of stimulation of different types of cones is interpreted by the brain as a specific colour * nocturnal animals have mostly rods * primates three different types of cones * dogs two types of cones * birds four populations of cones * the amount of colours perceived by different species is not clearly understood

Answer 43

Visual pathway Ganglion cell axons form the optic nerve 1. Primary visual cortex : involved in consciuos visual perception of form, color, motion, orientation and depth 2. Supracharismatic nucleus of the hypothalamus, plays a role in the regulation of physiological rythms by light dark cycle 3. Pretectal nucleus : plays a role in papillary refelxes of the eye, and reflex orientation of the eye to visual targets

Answer 44

Hearing Ear mediates the transduction of sound into action potentials **Outer ear** * pinna (auricle) * ear canal * external acoustic meatus funnels sound waves to the middle ear **Middle ear** * Tympanic membrane * middle ear **Inner ear** * cochlea * vestibular apparatus

Answer 45

Middle ear Structures Tympanic membrane * thin transparent membrane * junction between the external and middle ear * vibrates when sound energy enters the ear Middle ear * air filled cavity connected to the nasopahrynx by auditory tube * contains ossicles (malleus, incus, stapes) * contains two small muscular structures

Answer 46

Function of the middle ear The ossicles are all connected to each other The tympanic membrane is connected to the malleus - to the incus to the stapes to the oval window. The ossicles act to transfer the vibration of the ear drum to the oval window. Oval window - prevents a significant loss of energy as the sound wave is transferred from the air filled middle ear to the liquid filled inner ear. * sound wave energy is amplified from outer to inner ear *

Answer 47

The acoustic reflex Contraction of the muscles of the middle ear in response to loud sounds, acts to protect the ear and reduce the vibrations. It reduces the transfer of vibrations from the ear drum to the oval window.

Answer 48

Cochlea of the inner ear The cochlea has three chambers seperated by two membranes * Basilar membrane (floor of scala media, and organ of corti) * Organ of corti - has hair like receptor cells * Reissner's membrane Chambers * dorsally located scala vestibule * ventrally located scala tympani * middle scala media The scala vestibule and tympani contains **perilymph** the scala media contains **endolymph**

Answer 49

Transmission of sound waves within the cochlea * vibration of the oval window causes vibrations in the inner ear fluids * causes a series of traveling waves that begin at the base of basilar membrane and move along its length * organ of corti movements excites the hair cells * action potential travels along the eighth cranial nerve to the auditory cortex.