Special senses and endocrine system lecture 11&12

Question 1

special senses

Answer 1

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

Question 2

name the cranial nerves

Answer 2

Olfactory 
Optic 
Oculomotor
Trochlear 
Trigeminal** 
Abducens
Facial 
Accoustic*
Glossopharyngeal 
Vagus 
Spinal accessory  
Hypoglossal

Question 3

how to remember cranial nerves

Answer 3

on old olympus’ towering tops a Finn and German viewed some hops

Question 4

how to remember cranial nerves’ functions

Answer 4

some say marry money but my brother says big brains matter more

Question 5

taste

Answer 5

• 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

Question 6

types of papillae

Answer 6

Circumvallate or vallate papillae
• Large, round, least numerous (approx. 7-12)
Fungiform papillae
• Over entire tongue surface
• Mushroom shaped
Filiform papillae

Question 7

taste buds

Answer 7

• 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

Question 8

vagus nerve

Answer 8

• Sensory and motor

* Taste receptors in epiglottis and lower pharynx

Question 9

Glossopharyngeal nerve

Answer 9

• Sensory and motor

* Taste receptors in posterior third of tongue and pharynx

Question 10

facial nerve

Answer 10

• 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

Question 11

smell

Answer 11

• 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

Question 12

hearing

Answer 12

• Sensory cells: Hair cells (in organ of Corti in cochlea)
• Nerve: Auditory or vestibulocochlear (VIII)
• Brain processing: Auditory cortex in temporal lobe

Question 13

balance

Answer 13

• 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

Question 14

sight

Answer 14

• 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

Question 15

Specificity of response- hormonal vs nervpus system

Answer 15

• The nervous system targets organs precisely

* Hormones can have widespread effects (eg thyroid hormone, growth hormone)

Question 16

Speed of response- hormonal vs nervous system

Answer 16

• The nervous system (Lecture 9) typically responds to stimuli within milliseconds
• The endocrine system can take from several seconds to several days to respond

Question 17

Cessation of response- hormonal vs ns

Answer 17

• When a stimulus stops, the nervous system stops responding almost immediately
• Hormonal effects can last for several days, or longer

Question 18

Persistence of response- hormonal vs ns

Answer 18

• 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

Question 19

Long distance chemical signalling

Answer 19

Hormones
• Produced by the endocrine system
• Travel throughout the body via the blood
• Eg insulin

Question 20

Local chemical signalling

Answer 20

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

Question 21

endocrine system

Answer 21

• 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

Question 22

Stimulation via the blood

Answer 22

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))

Question 23

Stimulation via nerve fibres

Answer 23

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

Question 24

Endocrine organs

Answer 24

• Hypothalamus and pituitary glands
• Pineal gland
• Thyroid gland
• Parathyroid glands
• Adrenal glands
• Pancreas
• Thymus
• Gonads

Question 25

Hypothalamus

Answer 25

* 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)

Question 26

Pituitary

Answer 26

• Pituitary consists of two parts with separate developmental origins: – adenohypophysis (anterior three quarters) – neurohypophysis (posterior quarter)

Question 27

Neurohypophysis

Answer 27

* Posterior pituitary * Not a true gland * Actually part of brain * Neural tissue * Releases neurohormones (ie hormones secreted by neurons)

Question 28

Adenohypophysis

Answer 28

* Anterior pituitary * Glandular tissue * Releases hormones

Question 29

sphenoid

Answer 29

• 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)

Question 30

Anterior pituitary hormones

Answer 30

* Human Growth Hormone (hGH) * Thyroid Stimulating Hormone (TSH) or thyrotropin * Follicle-stimulating Hormone (FSH) * Lutenizing Hormone (LH) * Prolactin (PRL) * Adrenocorticotropin (ACTH) or corticotropin

Question 31

Posterior pituitary hormones

Answer 31

* Oxytocin (post-delivery hormone) | * Antidiuretic Hormone (ADH) or vassopressin

Question 32

pineal gland

Answer 32

• 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

Question 33

thyroid gland

Answer 33

• 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

Question 34

parathyroid gland

Answer 34

• 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

Question 35

adrenal glands

Answer 35

• 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)

Question 36

Adrenal medullary hormones

Answer 36

• Catecholamines (epinephrine and norepinephrine; increase heart rate, blood pressure and BMR)

Question 37

Adrenal cortical hormones

Answer 37

* Mineralcorticoids, including aldosterone (affects N a and K levels) * Glucocorticoids, including cortisol (regulates metabolism, resistance to stress) * Gonadocorticoids, including androgens (prepubertal growth, sex drive)

Question 38

cushing's syndrome

Answer 38

• 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

Question 39

pancreas

Answer 39

``` • 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 ```

Question 40

thymus

Answer 40

• 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)

Question 41

ovaries

Answer 41

• 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

Question 42

testes

Answer 42

``` • Testosterone – maturation of reproductive organs – secondary sex characteristics – sex drive – sperm production • Inhibin – inhibits FSH production ```

Question 43

heart

Answer 43

* 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

Question 44

kidneys

Answer 44

* Renin: converts angiotensin to angiotensin I | * Convert calcidiol to calcitriol (vitamin D3)

Question 45

stomach and small intestine

Answer 45

* Many enteric hormones, eg gastrin | * Other tissues and organs with endocrine cells include the skin, adipose tissue and the placenta

Question 46

liver

Answer 46

• 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