Medical Physiology: Endocrine & Reproductive Systems

Questions and Answers

What is the name of the feedback mechanism where the distance between the hypothalamus and the pituitary is short?

Positive feedback mechanism

Long negative feedback

Negative feedback loop

Short negative feedback (correct)

Which gland is primarily controlled by the nervous system?

Anterior lobe of the pituitary gland

Thyroid gland

Adrenal cortex

Adrenal medulla (correct)

What is an example of a hormone that stimulates secretion of another hormone without a target gland?

GHRH (correct)

Thyroid-stimulating hormone

FSH

What is the term for periodic variations in hormone secretion influenced by seasonal changes, development, and aging?

Cyclical variations of hormones Signup and view all the answers

Where are the receptors for thyroid hormones typically located?

In the cell nucleus Signup and view all the answers

What is the first step of a hormone's action?

Binding to specific receptors Signup and view all the answers

What is the importance of the shape of a receptor in hormone action?

It determines the binding affinity Signup and view all the answers

What is an example of a condition where there are no receptors for a hormone, leading to absence of secondary sex characteristics?

Feminizing testis Signup and view all the answers

What is the effect of estrogens on uterine blood flow?

Increases uterine blood flow Signup and view all the answers

What is the effect of estrogens on FSH?

Decreases FSH Signup and view all the answers

What is the effect of estrogens on bone growth?

Causes epiphysial closure in bones Signup and view all the answers

What is the effect of estrogens on libido?

Increases libido Signup and view all the answers

What are the targets of progesterone action?

Uterus, breasts, and brain Signup and view all the answers

What is the effect of progesterone on estrogen receptors in endometrium?

Decreases the number of estrogen receptors Signup and view all the answers

What is the effect of progesterone on breast development?

Stimulates development of breast’s lobules and alveoli Signup and view all the answers

What is the normal plasma progesterone level in females during luteal phase?

60 nmol/L Signup and view all the answers

What is the effect of increased prolactin levels on LH and FSH?

Inhibits LH and FSH production Signup and view all the answers

Which hormones are primarily secreted by the thyroid gland?

Thyroxine (T4) and Triiodothyronine (T3) Signup and view all the answers

What regulates the secretion of thyroid hormones?

Thyroid Stimulating Hormone (TSH) Signup and view all the answers

What is the primary effect of thyroid hormones on metabolism?

Increases cellular metabolic activity Signup and view all the answers

What is caused by excessive levels of thyroid hormone?

Diarrhea and increased appetite Signup and view all the answers

Which physiological action is NOT associated with thyroid hormones?

Decreased blood flow Signup and view all the answers

What effect do thyroid hormones have on carbohydrates?

Stimulate hepatic gluconeogenesis Signup and view all the answers

What is the basal metabolic rate (BMR) defined as?

Energy consumption at rest in optimal conditions Signup and view all the answers

What is the primary function of neurotransmitters?

To act locally on cell functions at synaptic junctions Signup and view all the answers

Which hormones are secreted by glands and transported through the blood?

Endocrine hormones Signup and view all the answers

What describes the function of cytokines?

Can function as autocrines, paracrines, or endocrine hormones Signup and view all the answers

How do target tissue cells recognize hormones?

Through special receptors designed for specific hormones Signup and view all the answers

What is the role of plasma proteins in relation to hormones?

To act as a storage site and buffer Signup and view all the answers

Which of the following is true regarding endocrine glands?

They discharge hormones directly into the bloodstream Signup and view all the answers

What distinguishes autocrines from paracrines?

Autocrines act on the same cell that secretes them Signup and view all the answers

Which hormone's targets consist of only specific target tissues?

Adrenocorticotropic hormone (ACTH) Signup and view all the answers

What physiological change is commonly associated with the loss of estrogen during menopause?

Hot flushes Signup and view all the answers

What role does FSH play in spermatogenesis?

Facilitates maturation of spermatids Signup and view all the answers

Which hormone primarily stimulates Leydig cells to produce testosterone?

LH Signup and view all the answers

Which of the following is a physiological action of testosterone?

Promotes male secondary sex characteristics Signup and view all the answers

What happens to primordial follicles around age 45?

They reach zero Signup and view all the answers

Which factor contributes to the physiological changes observed during menopause?

Decreased production of estrogens Signup and view all the answers

Which statement about testosterone biosynthesis is correct?

Synthesized from cholesterol in Leydig cells Signup and view all the answers

What is a common psychological symptom during menopause?

Fatigue Signup and view all the answers

Study Notes

Coordination of Body Functions

The activities of cells and organs are coordinated and controlled by the interaction of the nervous system and hormonal or endocrine system through the release of secretions:
- Neurotransmitters secreted by neurons in synaptic junctions and act locally on cell functions
- Endocrine hormones secreted by glands into the blood and act on cells in another location of the body
- Neuroendocrine hormones secreted by neurons into the blood and act on cells at another location in the body
- Paracrine hormones or substances secreted by cells into extracellular fluid and affect neighboring cells of a different type
- Autocrine hormones or substances secreted by cells into extracellular fluid and act on the function of the same cells that produced them
- Cytokines (e.g., interleukins) are peptides secreted by cells into extracellular fluid and function as autocrines, paracrines, or endocrine hormones

Target Tissue Cells

The endocrine hormones carried by blood to cells of the body called target tissue cells have special receptors for the action of the hormone
Types of target tissue cells:
- Many different types of cells of the body (e.g., growth hormone)
- Only specific target tissues (e.g., adrenocorticotropic hormone (ACTH))

Endocrine Glands

Defined as ductless glands that release their products directly into the blood circulation
Their products are called hormones, which are chemical substances produced by glands or neurosecretory cells
Hormones act as "chemical messengers"

Feedback Mechanisms

Short negative feedback: an example is the stimulation of secretion of growth hormone (GH) by growth hormone-releasing hormone (GHRH), which affects all body tissues, and there is no hormone released in response to it
Positive feedback mechanism: an increase in secretion of a particular hormone from a specific gland in response to an increase in a chemical substance (e.g., follicular-stimulating hormone (FSH) secreted by the pituitary gland, which circulates in the blood to affect the ovary in females)

Mechanism of Hormone Action

When a hormone binds to its receptor, it usually initiates a cascade of reactions in the cell
The first step of a hormone's action is to bind to specific receptors at the target cell, after dissociation of binding protein
Locations of hormone receptors:
- In or on the surface of cell membrane (mostly for protein, peptide, and catecholamine hormones)
- In the cell cytoplasm (found mainly in cytoplasm receptors for different steroid hormones)
- In the cell nucleus (receptors for thyroid hormones are found in the nucleus and are believed to be located in direct association with one or more of the chromosomes)

Thyroid Gland and its Hormones

The thyroid gland secretes two major hormones: thyroxine (T4) and triiodothyronine (T3), which are responsible for body metabolism
The thyroid gland also secretes calcitonin hormone, which is responsible for calcium metabolism
Thyroid gland hormones are controlled by thyroid-stimulating hormone (TSH)
Physiological actions of thyroid hormone:
- Increases transcription of large numbers of genes
- Increases cellular metabolic activity
- Increases heat production
- Increases O2 consumption and heat production
- Effects on carbohydrates, fat, and protein
- Effects on the cardiovascular system
- Effects on respiration
- Effects on the gastrointestinal system

Estrogens and Progesterone

Effects of estrogens on female genitalia:
- Increases uterine blood flow and uterine muscle
- Causes epiphysial closure in bones
- Causes salt and water retention
- Causes a significant plasma cholesterol-lowering action
- Increases libido
- Controls female secondary sex characteristics
Progesterone physiological actions:
- Responsible for progestational changes in the endometrium and cyclic changes in the cervix and vagina
- Has anti-estrogenic effects on the myometrial cells
- Decreases the number of estrogen receptors in the endometrium and increases the rate of conversion of estradiol to less active estrogens
- Stimulates development of breast lobules, alveoli, and supports secretory function of the breast during lactation

The Male Reproductive System

Hormonal control of spermatogenesis:
- The maturation of spermatids to spermatozoa depends on androgen acting on the Sertoli cells
- FSH acts on the Sertoli cells to facilitate the last stages of spermatid maturation
- FSH promotes production of Androgen Binding Protein (ABP)
Endocrine function of the testes:
- Testosterone is synthesized from cholesterol in the Leydig cells and is also formed from Androstenedione secreted by the adrenal cortex
- The biosynthetic pathways: direct pathway in Leydig cells and indirect pathway in the adrenal gland
- Testosterone physiological actions:
  - Acts during development of internal genitalia
  - Inhibitory negative feedback effect on pituitary LH
  - Development and maintenance of male secondary sex characteristics
  - Maintains spermatogenesis, along with FSH

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Description

Lectures on the coordination of body functions, including the role of the nervous and endocrine systems in controlling cellular and organ functions.