Reproductive Endocrinology Lecture Notes Flashcards
What in the nervous system regulates reproduction?
Simple neural reflexes and neuroendocrine reflexes
What in the endocrine system regulates reproduction?
Hormones
Differentiate neural reflexes from neuroendocrine reflexes.
In neural reflexes, a receptor detects a stimulus, and an afferent neuron transmits that information to the central nervous system, which determines the appropriate response. An efferent neuron then carries the response signal to the target tissue.
Neuroendocrine reflexes happen when a signal is sent from the spinal cord to the hypothalamus, which then releases hormones into the bloodstream, which then go to the target tissue.
What is the endocrine system and what are its three basic components?
An integrated network of multiple organs derived from different embryologic origins that release hormones ranging from small peptides to glycoproteins, which exert their effects either in neighboring or distant target cells. Components: endocrine glands, hormones, and target tissue.
Do endocrine glands have ducts?
No
Which endocrine glands are involved in reproduction?
Hypothalamus, pituitary, pineal, gonads, uterus, placenta
Where is the hypothalamus?
Located in the brain
Where is the pituitary? Describe it.
Located in the brain, composed of the anterior and posterior parts.
Describe the anterior pituitary (structure and function)
Includes the large pars distalis, the pars tuberalis, and the pars intermedia. It produces four tropic hormones that control other endocrine glands, as well as several other peptide hormones.
How does the anterior pituitary release hormones?
The hypothalamus produces releasing hormones (RHs) and inhibiting hormones (IHs), which are delivered to cells in the anterior pituitary by blood flowing through portal blood vessels in the pituitary stalk.
Describe the posterior pituitary (structure)
Includes the infundibular stalk and the pars nervosa.
How does the posterior pituitary release hormones?
Neurosecretory products of oxytocin- and vasopressin-synthesizing neurons are stored in axon terminals of the posterior pituitary, where they are released into the circulation upon neural stimulation.
Describe the function of the pineal gland.
It secretes melatonin during the dark phase of the light/dark cycle (circadian rhythm).
What does the photoneuroendocrine system do?
It integrates environmental cues with intrinsic circadian oscillators and consists of the pineal gland and the suprachiasmatic nucleus of the hypothalamus.
What are the gonadal hormones (there are seven)?
estrogen, progesterone, testosterone, relaxin, activin, inhibin, follistatin
What are the placental hormones (there are five)?
Human chorionic gonadotropin (hCG), equine chorionic gonadotropin (eCG/PMSG), estrogen, progesterone, placental lactogen
What is a hormone?
A chemical messenger synthesized and secreted by an endocrine gland, which circulates in body fluids and produces specific effects on the target tissue.
What are the functions of hormones?
Reproduction and sexual differentiation, development and growth, maintenance of the internal environment (homeostasis), and regulation of metabolism and nutrient supply.
What are the different ways hormones can be classified?
Source of production, biochemical structure, or mode of action
What are the seven different classes of hormones according to biochemical structure?
Peptides, polypeptides, proteins, glycoproteins, steroids, amines, and fatty acids.
Where are peptides synthesized/processed/released?
Synthesized as preprohormones in the ribosomes, processed to prohormones in the ER. Then packaged into vesicles in the Golgi. The vesicles are released from the cell in response to an influx of Ca2+.
What is the process of steroid hormone synthesis?
The StAR and TSPO transport cholesterol from the outer mitochondrial membrane (OMM) to the inner mitochondrial membrane (IMM), where cytochrome P450’s cholesterol side chain cleavage enzyme (P450scc) transforms cholesterol into pregnenolone, which will go to the smooth ER and be converted to progesterone or testosterone.
Describe prostaglandins and how they are synthesized.
Phospholipidases liberate arachidonic acid from membrane phospholipids. Arachidonic acid is then converted into prostaglandin H2 (PGH2) by cyclooxygenase. Other enzymes then create other forms of prostaglandin, which regulate several physiological functions such as contraction of smooth muscles in the reproductive tract, erection, ejaculation, sperm transport, ovulation, luteolysis, parturition, and milk ejection.
Where are peptides, proteins, and monoamines stored? What triggers their release?
They’re stored in secretory granules in endocrine cells. Signaling events triggered by exogenous regulators (termed secretagogues) causes their release.
Where are steroid hormones stored? How are their levels in the body controlled?
Steroid hormones are not stored to a significant degree in hormone-producing cells. Synthesis (rather than hormone release) appears to play the dominant role in controlling hormone levels in circulating plasma.
How are amines, peptides, and proteins transported?
They circulate in free form
How are steroids and thyroid hormones transported?
They’re bound to transport proteins
What is a ligand?
A chemical messenger released by one cell to signal either itself or a different cell
What is a receptor?
A protein molecule inside the target cell or on its surface that receive a chemical signal
What is signal transduction?
The intracellular transfer of information (biological activation/inhibition) through a signal pathway
What are the two types of receptors?
Cell surface receptors (e.g. peptide/protein hormone receptors) and intracellular/internal receptors (e.g. steroid hormone receptors)
What are second messengers?
Small molecules and ions that relay signals received by cell-surface receptors to effector proteins
What are the four classes of second messengers?
Cyclic nucleotides, lipids, ions, gases/free radicals
Differentiate between upregulation and downregulation
Upregulation: induction of greater than normal formation of receptor or intracellular signaling molecules by the target cell or greater availability of the receptor for interaction with the hormone.
Downregulation: Decrease in total receptor number in the cell due to increased hormone concentration and binding.
State the steps of the mechanism of protein hormone action.
- Hormone receptor binding
- Adenylate cyclase activation
- Protein kinase activation
- Synthesis of new products
State the steps of the mechanism of steroid hormone action with a FAST response.
- Steroid binding to membrane receptors
- Adenylate cyclase activation
- Protein kinase activation
- Changes in Ca2+ channel permeability
What are some examples of a fast response?
Estradiol causes ion channel alteration which causes an increase in myometrial contractions. Progesterone causes ion channel inhibition which causes a decrease in myometrial contractions.
State the steps of the mechanism of steroid hormone action with a SLOW response.
- Steroid transport
- Movement through the cell membrane and cytoplasm
- Binding of steroid to nuclear receptor
- mRNA and protein synthesis
What are some examples of a slow response?
Estradiol causes mucus secretion by female tract. Progesterone causes uterine gland secretion.
Differentiate between steroid and peptide/amine hormones in terms of storage pools
Steroid hormones do not have storage pools. Peptide/amine hormones are stored in secretory vesicles.
Differentiate between steroid and peptide/amine hormones in terms of interaction with the cell membrane
Steroid hormones diffuse through the cell membrane. Peptide/amine hormones bind to receptors on the cell membrane.
Differentiate between steroid and peptide/amine hormones in terms of receptor
Steroid hormone receptors are in the cytoplasm or nucleus. Peptide/amine hormone receptors are on the cell membrane.
Differentiate between steroid and peptide/amine hormones in terms of action
Steroid hormones primarily regulate gene transcription. Peptide/amine hormones cause signal-transduction cascades that affect a variety of cell processes.
Differentiate between steroid and peptide/amine hormones in terms of response time
Steroid hormones primarily take hours to days. Peptide/amine hormones take seconds to minutes.
What are agonists?
Analogs having a similar molecular structure that bind to the specific receptor and initially cause the same biologic effect as the native hormone
What are antagonists?
Analogs having greater affinity for the hormone receptor but promoting weaker biologic activity than the native hormone.
What is a hormone’s half-life?
The time required for one-half of a hormone to disappear from the blood or from the body.
Describe the steps of steroid hormone metabolism
Steroid is secreted by gonad and enters blood and goes to target tissue. It causes a change in the target tissue, and then passes (in the bloodstream) through the liver, where it’s rendered H2O soluble. It then reenters the blood and enters the kidney or bile, and is then excreted through feces or urine.
