Essay Questions

Question 1

Identify three examples of antagonistic hormonal processes. Briefly, present the physiological values specific to each of the antagonistic processes.

Answer 1

1. GH (Growth Hormone) and ACTH (Adrenocorticotropic) - GH stimulates growth, regeneration, and cellular reproduction, and is usually active at night; ACTH breaks things down and uses energy during times of stress and is usually active during the day. Antagonistic use of energy mobilization (ACTH) and storage (GH).
2. Insulin and Glucagon - Insulin transfers glucose out of blood and into hungry cells (unused glucose is converted to Glycogen and transferred for short-term storage in liver), while glucagon transfers glucose out of cells and into the blood when blood insulin levels are low. Following a meal, insulin is active, while glucagon is active in the fasting phase.
   * *both pancreatic hormones
3. Parathyroid hormone and calcitonin – when Ca2+ levels are low, PTH (from parathyroid glands) signals osteoclasts to degrade bone matrix and release calcium from bones/teeth back into the blood for use by brain and muscles; when Ca2+ levels are high, calcitonin (from thyroid gland) mobilizes calcium from the blood towards bones and teeth towards salt deposits in bone
4. Prolactin and estrogen - prolactin promotes lactation and produces milk in the mammary glands in response to giving birth, which antagonizes estrogen. The body suppresses the process of preparing for pregnancy and thus lowers its estrogen production. This is why lactation acts as a natural birth control.

Question 2

Discuss main regulatory processes controlling hormonal release into the circulatory system. Include in your answer various modes of stimulation that activate secretion by endocrine glands.

Answer 2

Hormones are usually secreted by ductless glands and distributed via the circulatory system. The main regulatory process controlling hormonal release is a negative feedback loop. The three types of stimuli that act as triggers…

1. Hormonal: hypothalamus secretes hormones that stimulate the anterior pituitary gland to secrete hormones released into the circulatory system that travels to other glands (thyroid gland, adrenal cortex, gonads) and stimulates them to secrete other hormones
2. Humoral: the trigger comes directly from the circulatory system, the low concentration of calcium ions stimulates the parathyroid glands to release parathyroid hormone (PTH) directly back into the circulatory system.
3. Neural: sympathetic NS arouses adrenal medulla, which then secretes catecholamines (adrenaline/norepinephrine); preganglionic SNS fiber stimulates adrenal medulla cells to secrete catecholamines

Question 3

How does the hypothalamus monitor hormonal production by the gonads (in both males and females)?

Answer 3

The hypothalamic-pituitary-gonadal axis (HPG axis) regulates hormonal production by the gonads via a humoral negative feedback loop. The hypothalamus monitors hormonal production by humorally receiving information from the circulatory system that we do not have enough (or have too many) sex hormones in the gonads. The hypothalamus then sends messages to the anterior pituitary gland (via gonadotropin-releasing hormone) to release (or inhibit) the release of gonadotropins. Gonadotropins are then carried by the circulatory system to the gonads, which release androgens, estrogens, and progestins.

In females, hormones go through a cycle that repeats itself every 28 days or so. In males, the gonadal and gonadotropic hormones change little from day to day.

According to this model, the brain controls the release of gonadotropin-releasing hormone from the hypothalamus into the hypothalamopituitary portal system, which carries it to the anterior pituitary. In the anterior pituitary, the gonadotropin-releasing hormone stimulates the release of gonadotropins, which are carried by the circulatory system to the gonads. In response to the gonadotropins, the gonads release androgens, estrogens, and progestins, which feed back into the pituitary and hypothalamus to regulate subsequent gonadal hormone release. Armed with this general perspective of neuroendocrine function, you are ready to consider how gonadal hormones direct sexual development and activate adult sexual behavior.

Question 4

Present the structure and the main physiological characteristics of the Pituitary Gland. How does the hypothalamus control the different parts of the pituitary?

Answer 4

o The Posterior Pituitary gland hormones are synthesized in the hypothalamus and stored in the posterior pituitary gland to be secreted. The posterior pituitary is composed of neurologic tissue and is a developmental extension of the hypothalamus. It secretes 2 hormones – ADH/vasopressin/antidiuretic hormone and oxytocin.

o The Anterior Pituitary gland synthesizes its own hormones. The anterior pituitary is controlled by releasing or inhibitory factors from the hypothalamus that signal the anterior pituitary via a circulatory pathway to make hormones. It is larger than the posterior pituitary and is composed of epithelial cells - embryologically, these cells migrated upwards from the roof of the mouth. It synthesizes 6 hormones - GH, prolactin, ACTH, TSH, LH, FSH.

Question 5

Present the steps of early sex differentiation (during embryonic and fetal development), with an emphasis on the role of hormones.

Answer 5

Organizing effects

1. Begins at fertilization of the ovum by the sperm with one of two zygotes, XX or XY
2. In early embryonic development, the gonads are primordial (undifferentiated)
3. At 7 weeks after conception, the SRY gene on the Y chromosome of the male triggers the production of SRY protein (Testis Factor)—causes the medulla of each primordial gonad to grow and develop into testis, or masculinization of gonads to testes (in absence, they grow into ovaries)
4. At 6 weeks after fertilization, both males and females have two complete reproductive tracts: Mullerian and Wolfian systems.
5. In the third month (~8 weeks) of male fetal development, the testes secrete testosterone, which converts to DHT and induces male scrotum and penis development, and Mullerian-inhibiting hormone, which inhibit female development (causing the Mullerian system to degenerate and the testes to descend into the scrotum); the development of the Mullerian system occurs in any fetus not exposed to testicular hormones during the critical fetal period

Question 6

Present the various parts of the Alimentary Canal and describe their main functions.

Answer 6

• The mouth begins the digestive process, with chewing (mastication) beginning the mechanical breakdown of food and enzymes in saliva starting to break down carbohydrates.
• The pharynx and esophagus propel food towards the stomach via peristalsis.
• Within the stomach, food is temporarily stored and hydrochloric acid and enzymes start the breakdown of proteins. Chyme, a mixture of semi-digested food with stomach acid, then is moved by peristalsis to the duodenum (the first part of the small intestine).
• Most digestion occurs within the small intestine, as pancreatic enzymes are released to break down carbs, fats, and proteins. Nutrients are absorbed into the bloodstream.
• Within the large intestine, absorption of minerals and waters occurs. Feces are lubricated and moved by peristalsis.
• Defecation occurs as feces exit the anal canal.

Question 7

What is the “Fight or Flight Response”? Describe the various neurological and hormonal processes involved in this systemic response.

Answer 7

• Role of the autonomic nervous system, amygdala, hypothalamus, pituitary gland, and adrenal gland
• We address threats with a quick decision to fight or flight (freeze has also been added as a response now)
• The autonomic nervous system is primarily involved (made up of sympathetic and parasympathetic)
• –>Reaction begins in the amygdala and triggers a neural response from the hypothalamus
• –>The pituitary gland is then activated which secretes ACTH (adrenaline)
• –>The adrenal gland is also activated via the sympathetic nervous system and releases epinephrine and/or norepinephrine which prepares us for fight or flight (Hormones involved in sympathetic nervous system: estrogen, testosterone, and cortisol; Neurotransmitters involved in sympathetic nervous system: dopamine and serotonin)
• –>Parasympathetic nervous system returns the body to homeostasis after fight or flight (Neurotransmitter involved: acetylcholine)

1. Starts with a stressful event - something that is interpreted as stressful based on a conversation between the cortex and limbic system
2. The amygdala interacts with the locus coeruleus, which is part of the reticular activating system, to increase alertness. This leads to activation of the HPA axis and stimulates release of ACTH, which stimulates release of cortisol from the adrenal cortex. Release of TSH from the anterior pituitary stimulates thyroxin from the thyroid gland, increasing metabolism.
3. The amygdala also stimulates the parabrachial nucleus to increase respiration and the periaqueductal gray area, which promotes an analgesic response.
4. Simultaneously, the hypothalamus also stimulates the sympathetic nervous system, which stimulates release of epinephrine and norepinephrine from the adrenal medulla.
5. In order to stop this process, the cortex and limbic system need to reinterpret the event and decide that it is no longer stressful. Hypothalamus stimulates parasympathetic system, anterior pituitary stops releasing hormones, and homeostatic equilibrium is re-established.

Question 8

What is osmotic thirst? What is hypovolemic thirst? How are these homeostatic imbalances corrected? (Your answer has to reflect an understanding of Homeostasis as a mechanism).

Answer 8

1. Osmotic thirst occurs when there is hypertonicity in the interstitial liquid environment (when the cellular environment is hypotonic). If not corrected, water will leave cells to osmotic pressure. Certain receptors detect cellular loss of water, which triggers a reduction of kidney secretion. In the brain, receptors (osmosensory neurons) in the OVLT (organum vasculosum laminae terminalis), an area anterior to the 3rd ventricle, is vasculated by blood capillaries and receives information from receptors in the stomach, detect high levels of salt (Na+) in the blood, stimulating two areas in the hypothalamus. Supraoptic nucleus and paraventricular nucleus control secretion of vasopressin, resulting in elevation of blood pressure and an antidiuretic response in the kidneys. Lateral preoptic area triggers thirst reaction and drinking. Kidneys secrete renin triggering a cascade culminating in release of aldosterone (steroid hormone from the adrenal cortex), directing kidneys to conserve Na+.
2. Hypovolemic thirst occurs when there is a drastic reduction of blood volume, resulting in low blood pressure, loss of salts in the body, and dehydration. Receptors trigger both physiological responses and drinking. Baroreceptors in the large veins and heart detect drop in blood pressure returning from the heart; such information reaches the hypothalamic regions described above (see osmotic thirst). These pressure receptors block heart secretion of ANP (atrial natriuretic peptide) which inhibits drinking, reduces blood pressure, and promotes kidneys’ excretion of water and salts (elevates potassium). Drop in blood volume detected by the kidneys, resulting in the secretion of renin; this hormone triggers the release of angiotensinogen which in turn triggers a chain of chemical reactions resulting in the following: constriction of blood vessels to elevate blood pressure; and stimulation of the SFO region in the brain (subfornical organ) which stimulates the preoptic area of the hypothalamus to release vasopressin (acting on the kidneys to reduce water loss) and triggering thirst reaction.

Question 9

Describe the ovarian (menstrual) cycle. Your answer must present the events of this cycle as the result of a systemic interplay between the hypothalamic-pituitary axis and the internal female sex organs.

Answer 9

The menstrual cycle is controlled by negative feedback loops in the HPG axis.
During the menstrual cycle, the hypothalamus secretes releasing hormones controlling the secretion of FSH and LH by the anterior pituitary gland.
• During the follicular phase (menstrual phase), the body sheds the functional layer of the endometrium. At this point, hormone levels are relatively low so the circulatory system humorally tells the hypothalamus that more hormones are needed. The hypothalamus tells the anterior pituitary to release FSH, which stimulates follicle development and the secretion of estrogen by the growing ovarian follicles.
• During the second part of the follicular phase (proliferative phase), the follicles start to become mature ova and secrete more estrogen - causing the endometrium to return to its functional level. In response to the proliferation of estrogen, the hypothalamus tells the anterior pituitary to secrete LH. The sudden surge of LH causes one or more ova to rupture the membrane of the ovaries and travel down the fallopian tube (ovulation).
• During the luteal (secretory) phase, LH triggers the corpus luteum to secrete progesterone to enrich the endometrium for fertilization. If fertilization does not occur, the corpus luteum degenerates, ovarian hormones decline, and the endometrium crumples - initiating menses.

“The preparation of the ovarian follicle is done through a positive-feedback loop that involves both estrogen and LH. Release of the ovarian follicle into the uterus leads to the production of progesterone from the ovary. Progesterone has a negative effect on the positive-feedback loop of estrogen and LH as it inhibits the hypothalamus and consequently the anterior pituitary. This production of progesterone from the ovary is taken over by the fetus if conception occurs. If it does not occur, the level of progesterone in the bloodstream decreases and this decreases the negative-feedback on the hypothalamus, which allows it to produce GnRH and thus stimulate the anterior pituitary to produce and release FSH and LH, preparing the female for the preparation of the next ovarian follicle.”

Question 10

Present the major and minor nutrient groups. Give specifics regarding their source and availability in various foods.

Answer 10

Major Nutrient Groups

1. Carbohydrates
   - sugars, glycogen and starch
   - all carbs derive from plants (except for milk sugar or lactose and small amounts of glycogen in meats)
   - polysaccharide starch are mostly in grains, legumes, and root vegetables
   - polysaccharide cellulose found in most vegetables are not digested by humans, but provide roughage (aids defecation)
2. Lipids
   - most dietary lipids are triglycerides (neutral fats), but we also digest cholesterol and phospholipids
   - saturated fats come from animal products (meat and dairy) or some plants, like coconut
   - unsaturated fats can be found in seeds, nuts, and most vegetable oils
   - cholesterol can be found in dairy products, meats and egg yolk
3. Proteins
   - best quality of proteins can be found in meat products
   - complete proteins (providing the body with all amino acid requirements for tissue maintenance and growth) are found in eggs, milk, fish and most meats
   - Essential amino acids (9 in adults and 10 in infants) that our body cannot make, must come from our diet (Vegetarians need to be careful because some plant products (legumes such as beans and peas, nuts and cereals) are rich in proteins, but missing one or two essential amino acids; therefore, diet needs to be planned to obtain all amino acids (i.e. legumes and grains; beans and rice))
4. Water

Minor Nutrient Groups

1. Vitamins
   - function as coenzymes
   - organic nutrients that the body requires in small amounts can be found in most major food groups ( no one food has all the vitamins) requiring a balanced diet
   - Vitamins A, C, and E have anticancer properties) A and C are richly supplied by broccoli, cabbage and Brussel sprouts (lots of controversies about the ability of vitamins)
2. Minerals
   - we need seven types of minerals (inorganic substances), with traces of others (about a dozen)
   - fats and sugars have no minerals
   - cereal and grains have a few, but they are poor sources; mineral rich foods are vegetables, legumes, milk, and some meats
   - we need calcium, phosphorus, potassium, sulfur, sodium, chloride and magnesium

Question 11

Describe the classical four types of learning. Identify one important brain region or neurophysiological process and its contribution for each type of learning.

Answer 11

1. Stimulus-response learning: making connections; Classical conditioning or S-S associations leading to reflexive actions, and Operant conditioning, or S-R associations leading to shaping or extinguishing behaviors. Reinforcements – cause behavioral changes and probabilities of occurrences; amygdala is important for CC (e.g. reactions to aversive stimuli; autonomic/visceral reactions to stimuli); the interface between memory and emotion; involvement of the amygdala by modulating memory by emotional experiences
2. Motor learning: driving a car, biking, listening to a lecture and taking notes; basal ganglia is important for the acquisition of nondeclarative memories involved in motor learning; cortex is also involved in motor learning (component of S-R learning); connections between the cerebellum, thalamus, basal ganglia, and motor cortices; basal ganglia important for operant conditioning—actions consequent to interactions with environment; e.g., skilled driving); acquisition of nondeclarative memories
3. Perceptual learning: recognition and categorization of objects and situations, leading to behaviors and change (involves all the of the above), sensory processes; connections between the cortex, thalamus, parietal cortices and limbic system; connections between cortex (specific and multisensory)
4. Relational learning: complex learning, multimodal integration; learning relationships and/or connections between stimuli; includes spatial learning (not sensory/perceptual specific; includes multimodal integration – associative cortical activity); hippocampus involved in the consolidation and reconsolidation of declarative memory; other areas of the brain involved include the fornix, mammillary bodies, hypothalamus and cortex

Question 12

What are the main differences between the hippocampus and the basal ganglia in their contribution to memory processes? What kind of dysfunctions will result from insults to these brain structures?

Answer 12

1. Basal ganglia: number one subcortical structure involved in procedural memory (nondeclarative); implicit memory, ability; habitual, skilled, nonverbal; if dysfunction, you can talk about doing the thing, but you can’t actually do it; BG is involved in learning associations between stimuli and outcome and helping selecting from alternative responses based on stimuli received from different parts of the brain
2. Hippocampus: very important for declarative memory (seeing a picture and talking about it); mostly verbal; if dysfunction, you can ride a bike, but if asked about riding a bike you’d say “what? What is a bike?”; the hippocampus binds together information coming from many modalities and has the specific index for specific elements of the memorized event, cuing where the information is stored

Question 13

What are structural and functional aspects of language? In your attempt to explain the values of these aspects, provide specific examples of functional and dysfunctional manifestations for each of these factors of language.

Answer 13

• Language comprehension in the association areas include the superior temporal sulcus (STS) including Heschl gyrus, insula, and Wernicke’s area
• Medial temporal area links language to limbic structures (association with attention, learning, memory, and emotion)
• Ventral-lateral integrates with ventral visual stream (integrating object recognition with verbal and visual LTM)
• Connections to other areas such as Broca’s area and frontal regions, connections with integrating ventral and dorsal visual streams

Question 14

Describe the main functions of the muscles?

Answer 14

a. Producing Movement – almost all movements in the body (mobility, manipulation, quick responses to environmental events, emotional expressions, mobilization of visceral organs and motility of fluids and substances) are produced by muscles.
b. Maintaining Posture – we are usually unaware how the skeletal muscles are continuously making numerous tiny adjustments to maintain appropriate posture in response to the force of gravity.
c. Stabilizing Joints – a by product of the harmonious relationships between muscle, tendons and bones.
d. Generating Heat – as ATP (adenosine triphosphate provides a form of chemical energy used by cells) powers muscle contractions, about ¾ of its energy escapes as heat. Heat is vital in maintaining body temperature. Skeletal muscles activity is responsible for 40% of body heat.