Special senses and endocrine system lecture 11&12 Flashcards
special senses
Taste, Smell, Hearing, Balance, Sight special senses – have specialised sensory cells – are located in the head – are innervated by cranial nerves – have specialised associated anatomical structures
name the cranial nerves
Olfactory Optic Oculomotor Trochlear Trigeminal** Abducens Facial Accoustic* Glossopharyngeal Vagus Spinal accessory Hypoglossal
how to remember cranial nerves
on old olympus’ towering tops a Finn and German viewed some hops
how to remember cranial nerves’ functions
some say marry money but my brother says big brains matter more
taste
• Sensory cells: Gustatory cells (with supportive cells in taste bud)
• Nerve(s): Facial, Glossopharyngeal, Vagus
(NB because taste involves three different nerves, taste disorders are less common than smell disorders, since the system is less likely to be put completely out of business)
• Brain processing: Gustatory cortex
types of papillae
Circumvallate or vallate papillae • Large, round, least numerous (approx. 7-12) Fungiform papillae • Over entire tongue surface • Mushroom shaped Filiform papillae
taste buds
• Taste buds are found mainly on on the tops of fungiform papillae, and in the epithelium of the side walls of the foliate and circumvallate papillae
• Taste buds consist of 50-100 epithelial cells
– gustatory (taste) cells
– basal cells
• Taste buds are routinely burned by hot food, but are replaced every 7-10 days, by basal cells acting as stem cells
vagus nerve
- Sensory and motor
* Taste receptors in epiglottis and lower pharynx
Glossopharyngeal nerve
- Sensory and motor
* Taste receptors in posterior third of tongue and pharynx
facial nerve
- Sensory and motor
- Taste receptors in anterior two thirds of tongue
- These afferent fibres synapse in the solitary nucleus of the medulla, and then to gustatory cortex via thalamic nucleus
- As taste impulses pass through the solitary nucleus, they initiate parasympathetic responses associated with salivation and digestion
smell
- Sensory cells: Olfactory cells (plus supporting cells in olfactory epithelium)
- Nerve: Olfactory nerve (I)
- Brain processing: Olfactory bulb
- Note that the olfactory nerve has a single function, and it is the only nerve involved in that function; all of the processing occurs in one part of the brain
- Contrast this with taste: three nerves, more than one function for these nerves
hearing
- Sensory cells: Hair cells (in organ of Corti in cochlea)
- Nerve: Auditory or vestibulocochlear (VIII)
- Brain processing: Auditory cortex in temporal lobe
balance
- Sensory cells: Hair cells (cupula of vestibules of semicircular canals)
- Nerve: Auditory or vestibulocochlear (VIII)
- Brain processing: Cerebellum
- Note: one nerve, two functions (balance and hearing)
- The auditory nerve picks up information relating to both hearing and balance and transmits it to two parts of the brain
- Blows to the back of the head and therefore cerebellum can cause balance problems, and the appearance of drunkenness
sight
- Sensory cells: Rods and cones in retina
- Nerve: Optic (II)
- Brain processing: Visual cortex in occipital lobe
- Again, the nerve has a single function, and it is the only nerve involved in that function; all of the processing occurs in one part of the brain
Specificity of response- hormonal vs nervpus system
- The nervous system targets organs precisely
* Hormones can have widespread effects (eg thyroid hormone, growth hormone)
Speed of response- hormonal vs nervous system
- The nervous system (Lecture 9) typically responds to stimuli within milliseconds
- The endocrine system can take from several seconds to several days to respond
Cessation of response- hormonal vs ns
- When a stimulus stops, the nervous system stops responding almost immediately
- Hormonal effects can last for several days, or longer
Persistence of response- hormonal vs ns
- With repeated stimulation, neurons adapt and their response declines
- The endocrine system is more persistent: eg, thyroid hormone levels increase in cold weather and remain high as long as it remains cold
Long distance chemical signalling
Hormones
• Produced by the endocrine system
• Travel throughout the body via the blood
• Eg insulin
Local chemical signalling
Paracrines
• Affect cell types other than those releasing them
• Eg some pancreatic cells release somatostatin, inhibiting insulin release in a different population of pancreatic cells
Autocrines
• Exert effects on the same cells that secrete them
• Eg certain prostaglandins produced by smooth muscle cells cause those smooth muscle cells to contract
endocrine system
• Endocrine glands (ductless glands) release
hormones into interstitial fluid (ultimately into
circulatory system)
• Exocrine glands secrete into ducts (salivary
glands are an example)
• Note similarity to nervous system in which
neurons release neurotransmitters
Stimulation via the blood
Humoral stimulation
• Some hormones are released in direct response to changes in levels of ion or nutrients in blood
Hormonal stimulation
• Other hormones (eg hypothalamus releases hormones stimulating release of anterior pituitary hormones, which in turn stimulate other endocrine glands (eg thyroid, adrenal cortex, gonad))
Stimulation via nerve fibres
Neural stimulation
• In a few instances, hormone release is stimulated by nerve fibres; eg sympathetic nervous system causes adrenal medulla to release norepinephrine and epinephrine
Endocrine organs
- Hypothalamus and pituitary glands
- Pineal gland
- Thyroid gland
- Parathyroid glands
- Adrenal glands
- Pancreas
- Thymus
- Gonads
Hypothalamus
- Hypothalamus forms the floor and walls of third ventricle of brain
- Hypothalamus regulates water balance, sex drive and many other functions via interactions with the pituitary gland (hypophysis)
Pituitary
• Pituitary consists of two parts with separate developmental origins:
– adenohypophysis (anterior three quarters)
– neurohypophysis (posterior quarter)
Neurohypophysis
- Posterior pituitary
- Not a true gland
- Actually part of brain
- Neural tissue
- Releases neurohormones (ie hormones secreted by neurons)
Adenohypophysis
- Anterior pituitary
- Glandular tissue
- Releases hormones
sphenoid
• Butterfly-shaped
• Keystone of cranium; articulates with all other cranial bones
• Central body with three paired processes:
– greater wings
– lesser wings
– pterygoid processes
• Superior surface bears sella turcica (‘Turk’s saddle’), in which sits hypophysis (pituitary)
Anterior pituitary hormones
- Human Growth Hormone (hGH)
- Thyroid Stimulating Hormone (TSH) or thyrotropin
- Follicle-stimulating Hormone (FSH)
- Lutenizing Hormone (LH)
- Prolactin (PRL)
- Adrenocorticotropin (ACTH) or corticotropin
Posterior pituitary hormones
- Oxytocin (post-delivery hormone)
* Antidiuretic Hormone (ADH) or vassopressin
pineal gland
• The pineal gland secretes melatonin at night (a monamine) from serotonin
• This fluctuates with seasonal changes in day length
• In animals with seasonal breeding, this
regulates reproductive state
• Function of pineal gland in humans is
obscure; it may be involved in circadian
rhythm and some mood disorders
• Melatonin levels are elevated in premenstrual syndrome and in seasonal affective disorder
thyroid gland
• Located on trachea, just inferior to larynx
• Two lateral lobes connected by isthmus
• Largest pure endocrine gland in body
• Extremely well supplied with blood (superior and inferior thyroid arteries), so thyroid surgery is extremely complicated
• About 50% of people have an extra,
pyramidal lobe growing up from the isthmus
• Others lack an isthmus, or have thyroid
tissue in the root of the tongue or elsewhere in the neck
• Thyroxine, calcitonin
parathyroid gland
• Tiny glands on posterior of thyroid
• Usually four, but may be up to eight, and
some may be located elsewhere in neck or
even thorax
• Produce parathyroid hormone (PTH, or parathormone), a protein hormone controlling
calcium levels in blood
adrenal glands
• Located on top of kidneys
• Structurally and functionally, each adrenal gland comprises two endocrine glands, each
producing its own set of hormones:
– inner adrenal medulla (part of sympathetic nervous system)
– outer adrenal cortex (glandular tissue)
Adrenal medullary hormones
• Catecholamines (epinephrine and norepinephrine; increase heart rate, blood pressure and BMR)
Adrenal cortical hormones
- Mineralcorticoids, including aldosterone (affects N a and K levels)
- Glucocorticoids, including cortisol (regulates metabolism, resistance to stress)
- Gonadocorticoids, including androgens (prepubertal growth, sex drive)
cushing’s syndrome
• Caused by adrenal tumor or tumor that
stimulates adrenocorticotropic hormone (ACTH) causing overproduction of cortisol by adrenal cortex
• Symptoms include tendency to gain weight, acne, growth of facial hair
• Iatrogenic Cushing’s Syndrome can be
caused by taking steroids
pancreas
• Spongy gland located below and behind the stomach • Critical in digestion Secretes: • Glucagon – 29aa polypeptide; increases blood glucose – 1 molecule of glucogen can release 100 million glucose molecules into blood) • Insulin – 51aa protein; decreases blood glucose
thymus
• Part of both endocrine and lymphatic systems
• Located between heart and base of neck
• Firm and conical in children; red due to rich blood supply
• After age 15 or so, contains less lymphatic
tissue and shrinks; becomes yellowish as it accumulates fat
• By old age, difficult to distinguish from
surrounding fat
• Site of maturation of T lymphocytes
• Hormones that promote T-cell proliferation
(involved in immune system)
ovaries
• Oestrogens
– Maturation of reproductive organs
– Appearance of secondary sex characteristics at puberty
• Progesterone
– breast development, control of menstrual
cycle (in combination with oestrogens)
• Also inhibin and relaxin
testes
• Testosterone – maturation of reproductive organs – secondary sex characteristics – sex drive – sperm production • Inhibin – inhibits FSH production
heart
- High blood pressure stretches heart wall, stimulating atrial muscle to produce atrial natriuretic peptide (ANP)
- ANP increases urine output and sodium excretion, and inhibits angiotensin II: this lowers blood pressure
kidneys
- Renin: converts angiotensin to angiotensin I
* Convert calcidiol to calcitriol (vitamin D3)
stomach and small intestine
- Many enteric hormones, eg gastrin
* Other tissues and organs with endocrine cells include the skin, adipose tissue and the placenta
liver
• Angiotensin: converted by kidneys, lungs and other organs to angiotensin II, which
regulates blood pressure)
• Calcidiol
• Hepcidin: role in iron homeostasis
• Insulin-like growth factor (IGF): mediates
growth hormone action
• Erythropoietin (EPO): stimulates red blood
cell production
