Hypothalamus and Pituitary Gland Overview

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Questions and Answers

What is the primary function of the hypothalamus?

Controlling body temperature

Facilitating digestion

Regulating blood pressure

Maintaining homeostasis (correct)

Which hormone is known as antidiuretic hormone?

Cortisol

Arginine-vasopressin (correct)

Adrenaline

Oxytocin

What type of hormones does the hypothalamus produce that affect the anterior pituitary?

Steroid hormones

Growth factors

Regulatory hormones (correct)

Neurotransmitters

Which gland is referred to as the 'master control gland'?

Pituitary gland Signup and view all the answers

What significant role does oxytocin play during labor?

It initiates uterine contractions. Signup and view all the answers

In which part of the body is the pituitary gland located?

Inside the skull Signup and view all the answers

What connects the hypothalamus directly to the pituitary gland?

Blood vessels Signup and view all the answers

What is one of the primary functions regulated by the hypothalamus?

Hunger Signup and view all the answers

What is the primary hormone secreted by somatotrophs?

Growth hormone (GH) Signup and view all the answers

What causes the secretion of prolactin to increase?

Suckling Signup and view all the answers

How does somatostatin affect growth hormone (GH) release?

It inhibits GH release. Signup and view all the answers

What is the result of excess adrenocorticotrophic hormone (ACTH) secretion due to pituitary tumors?

Cushing's disease Signup and view all the answers

What effects does growth hormone (GH) have on metabolism?

It stimulates amino acid and fatty acid metabolism. Signup and view all the answers

What condition may result from GH insufficiency in children?

Short stature (dwarfism) Signup and view all the answers

What is the role of corticotrophs in the anterior pituitary?

They synthesize adrenocorticotrophic hormone (ACTH). Signup and view all the answers

What hormonal effect does dopamine have on prolactin secretion?

It inhibits prolactin release. Signup and view all the answers

What effect does MSH have on the skin?

Stimulates pigmentation of skin Signup and view all the answers

Which hormone is released by corticotrophs?

Melanocyte-stimulating hormone (MSH) Signup and view all the answers

What is the role of β-Lipotrophin?

Converted into endorphins for pain control Signup and view all the answers

What do LH and FSH primarily control?

Development of germ cells and sex hormone secretion Signup and view all the answers

What stimulates the release of TSH?

Stress via the central nervous system Signup and view all the answers

What is released by the posterior pituitary?

Antidiuretic hormone (ADH) and oxytocin Signup and view all the answers

What is the consequence of LH and FSH deficiencies in adults?

Infertility Signup and view all the answers

What is true about chromophobes in the pituitary gland?

They are active secretory cells Signup and view all the answers

What percentage of the pituitary gland must be destroyed before symptoms of hypopituitarism typically become apparent?

70% Signup and view all the answers

Which condition may present early symptoms of amenorrhoea and infertility in hypopituitarism?

Gonadotrophin deficiency Signup and view all the answers

What is the term for the condition involving the deficiency of all pituitary hormones?

Panhypopituitarism Signup and view all the answers

Which organ's function is primarily affected by ACTH deficiency?

Adrenal gland Signup and view all the answers

What may cause growth retardation in children as a consequence of hypopituitarism?

GH deficiency Signup and view all the answers

What is a likely clinical feature of secondary hypogonadism in adults?

Amenorrhoea Signup and view all the answers

Which deficiency may be clinically indistinguishable from primary hypothyroidism?

TSH deficiency Signup and view all the answers

In cases where pituitary function is affected by a tumor, what hormone is often raised?

Prolactin Signup and view all the answers

What is the purpose of measuring plasma concentrations of LH, FSH, and oestradiol or testosterone?

To confirm hormonal deficiencies Signup and view all the answers

What should be investigated if plasma concentrations of the target gland hormone are low while trophic hormone concentrations are raised?

The ovaries or testes Signup and view all the answers

Why is the insulin stimulation test considered potentially dangerous?

It can induce severe hypoglycaemia Signup and view all the answers

What is a significant expected rise in plasma cortisol concentrations during an insulin stimulation test?

More than 200 nmol/L Signup and view all the answers

Which hormone's levels are assessed during both the insulin stimulation test and the glucagon stimulation test?

Cortisol Signup and view all the answers

What is a key feature of the glucagon stimulation test?

It stimulates GH and ACTH release Signup and view all the answers

What role does imaging play in the investigation of hypopituitarism?

It may help identify a cause of hypopituitarism Signup and view all the answers

When preparing for an insulin stimulation test, what is the first step after inserting the intravenous cannula?

Take basal blood samples Signup and view all the answers

What is one of the main functions regulated by the hypothalamus?

Temperature regulation Signup and view all the answers

Which hormone is transported to the posterior pituitary for storage?

Oxytocin Signup and view all the answers

What is the primary role of releasing hormones produced by the hypothalamus?

To stimulate anterior pituitary hormone secretion Signup and view all the answers

How does the hypothalamus communicate with the anterior pituitary gland?

Via a direct blood supply Signup and view all the answers

Which part of the pituitary gland is responsible for storing hormones produced by the hypothalamus?

Posterior pituitary Signup and view all the answers

In what location is the pituitary gland located in relation to other anatomical structures?

Inside the skull, below the brain Signup and view all the answers

Which statement best describes the function of the pituitary gland?

It produces and controls hormones for most endocrine glands Signup and view all the answers

What is the primary function of growth hormone (GH) secreted by somatotrophs?

Stimulates long bone and soft tissue growth Signup and view all the answers

What type of hormones produced by the hypothalamus function to inhibit anterior pituitary secretion?

Inhibitory hormones Signup and view all the answers

What is one common result of hypersecretion of prolactin?

Galactorrhoea Signup and view all the answers

Which hormone is classified as a precursor synthesized by corticotrophs?

Pro-opiomelanocortin (POMC) Signup and view all the answers

What physiological condition can arise from a deficiency of adrenocorticotrophic hormone (ACTH)?

Glucocorticoid deficiency Signup and view all the answers

The release of TAG (triglycerides) by lactotrophs is inhibited by which substance?

Dopamine Signup and view all the answers

How does the secretion of ACTH respond to stress?

Pulsatile increase in secretion Signup and view all the answers

What is the condition resulting from GH insufficiency in children called?

Short stature (dwarfism) Signup and view all the answers

What physiological stimulus leads to the release of GHRH (growth hormone releasing hormone)?

Hypoglycaemia Signup and view all the answers

Which hormones should be measured to assess pituitary hormone secretion after maximal stimulation?

LH, FSH, and oestradiol or testosterone Signup and view all the answers

What indicates a potential deficiency in the target gland when plasma hormone concentrations are low but trophic hormones are raised?

Further investigation of the target gland is necessary Signup and view all the answers

In the insulin stimulation test, what is the primary purpose of lowering plasma glucose concentrations?

To trigger symptomatic hypoglycemia Signup and view all the answers

What is a significant cortisol response expected during an insulin stimulation test?

Cortisol should rise by more than 200 nmol/L Signup and view all the answers

Which condition could the glucagon stimulation test help differentiate from pseudo-Cushing's syndrome?

Cushing’s syndrome Signup and view all the answers

What imaging technique may help elucidate a cause of hypopituitarism?

CT or MRI scanning Signup and view all the answers

Why must the insulin stimulation test be conducted under direct medical supervision?

Due to the risk of severe hypoglycemia Signup and view all the answers

What initiates the glucagon stimulation test?

Fasting overnight followed by intravenous glucagon injection Signup and view all the answers

What hormones are secreted by gonadotrophs?

Follicle stimulating hormone (FSH) and luteinizing hormone (LH) Signup and view all the answers

Which subunit of the gonadotrophins is common to follicle stimulating hormone (FSH) and luteinizing hormone (LH)?

Alpha subunit Signup and view all the answers

What stimulates the release of thyrotropin (TSH)?

Thyrotrophin releasing hormone (TRH) Signup and view all the answers

What is the effect of negative feedback on TSH release?

Inhibits TSH release Signup and view all the answers

What is the main consequence of deficiencies in LH and FSH levels?

Infertility in adults and lack of sexual maturation in children Signup and view all the answers

What role does β-Lipotrophin play after its conversion?

Acts as a neuropeptide for pain control Signup and view all the answers

How does the secretion of TSH exhibit its rhythm?

Pulsatile release with a diurnal rhythm Signup and view all the answers

Which statement about chromophobes is accurate?

They contain secretory granules and can secrete hormones like prolactin. Signup and view all the answers

What is a common cause of growth retardation in children with hypopituitarism?

Deficiency of GH Signup and view all the answers

Which condition is a consequence of secondary hypogonadism in adults?

Amenorrhoea Signup and view all the answers

What is indicated by secondary adrenocortical hypofunction in hypopituitarism?

Hypotension Signup and view all the answers

Which pituitary hormone deficiency may lead to failure to lactate?

Prolactin Signup and view all the answers

In hypopituitarism due to a tumor, what is often observed with plasma prolactin concentrations?

Galactorrhoea Signup and view all the answers

What characterizes panhypopituitarism?

Deficiency of all pituitary hormones Signup and view all the answers

Which hormonal deficiency may mimic primary hypothyroidism clinically?

TSH deficiency Signup and view all the answers

What is typically required for the investigation of suspected hypopituitarism?

Assessing target gland hormone levels Signup and view all the answers

What major effect does growth hormone (GH) primarily have on the body?

Promotes growth of long bones and soft tissue Signup and view all the answers

What is the effect of somatostatin on the release of growth hormone (GH)?

Inhibits the secretion of GH Signup and view all the answers

Which condition is associated with excess production of adrenocorticotrophic hormone (ACTH)?

Cushing's disease Signup and view all the answers

What triggers increased secretion of prolactin following childbirth?

Suckling by the infant Signup and view all the answers

Which factor is known to inhibit the secretion of prolactin?

Dopamine from the hypothalamus Signup and view all the answers

What effect does stress have on the secretion of adrenocorticotrophic hormone (ACTH)?

Stimulates ACTH secretion Signup and view all the answers

What condition may result from a deficiency of prolactin secretion?

Lactation failure Signup and view all the answers

What is a major consequence of growth hormone insufficiency in children?

Short stature (dwarfism) Signup and view all the answers

What triggers the secretion of antidiuretic hormone (ADH) from the hypothalamus?

Increased plasma osmolality Signup and view all the answers

What is a potential consequence of a defect in ADH action?

Diabetes insipidus Signup and view all the answers

Which therapeutic application is associated with oxytocin?

Inducing labor Signup and view all the answers

What mechanism modifies the secretion of pituitary hormones under stress?

Direct neuronal stimuli Signup and view all the answers

What is the primary method of feedback control for pituitary hormone secretion?

Concentration of circulating target cell hormones Signup and view all the answers

How does increased prolactin secretion occur in response to dopamine antagonism?

By reducing inhibitory effects on prolactin secretion Signup and view all the answers

What rhythmic pattern characterizes the release of hypothalamic and pituitary hormones?

Intermittent pulses or circadian rhythms Signup and view all the answers

What action does bromocriptine have on prolactin secretion?

It decreases prolactin levels Signup and view all the answers

What does a serum concentration of both low target gland hormone and low-normal trophic hormone suggest?

Need for a pituitary stimulation test Signup and view all the answers

What is the main indication for conducting an insulin stimulation test?

Assessment of GH in growth deficiency Signup and view all the answers

During an insulin stimulation test, what is the expected increase in plasma cortisol if the response is adequate?

More than 200 nmol/L Signup and view all the answers

What are the primary hormones measured in the glucagon stimulation test?

GH and ACTH Signup and view all the answers

Which hormone is indicative of adrenocortical insufficiency when assessed at 09.00 h?

Cortisol Signup and view all the answers

What role do imaging techniques like CT or MRI serve in the context of hypopituitarism?

They help elucidate causes of hypopituitarism Signup and view all the answers

What is the requirement for performing the insulin stimulation test safely?

It should be done under direct medical supervision Signup and view all the answers

What should be investigated if plasma concentrations of target gland hormone are low while trophic hormone concentrations are raised?

Secondary gland disease Signup and view all the answers

What clinical feature is commonly associated with deficiency of gonadotrophins in adult males?

Loss of secondary sexual characteristics Signup and view all the answers

Which consequence of pituitary hormone deficiency could lead to an increased risk of hypotension?

ACTH deficiency Signup and view all the answers

What cardinal symptom might present in a child experiencing growth retardation due to hypopituitarism?

Height below expected percentiles Signup and view all the answers

In the context of pituitary hormone deficiencies, when might plasma concentrations of ACTH and/or TSH remain normal?

In the early stages of hypopituitarism Signup and view all the answers

What is a potential effect of GH deficiency in adults?

Increased insulin sensitivity Signup and view all the answers

Which type of hypopituitarism involves the deficiency of all pituitary hormones?

Panhypopituitarism Signup and view all the answers

What triggers the release of LH and FSH during reproductive life?

Gonadotrophin releasing hormone (GnRH) Signup and view all the answers

Which two hormones are synthesized in the posterior pituitary?

ADH and oxytocin Signup and view all the answers

What condition might develop due to prolactin deficiency following postpartum pituitary infarction?

Failure to lactate Signup and view all the answers

Which of the following factors may result in hypopituitarism?

Head injury Signup and view all the answers

What is the role of the β subunit in gonadotrophins?

Important for receptor recognition Signup and view all the answers

What effect does excess secretion of LH and FSH have in children?

Precocious puberty Signup and view all the answers

How does TSH influence thyroid function?

Stimulates the production of T3 and T4 Signup and view all the answers

Which hormones are primarily affected by negative feedback from T3 and T4?

TSH and TRH Signup and view all the answers

What consequence might arise from a deficiency of β-Lipotrophin?

Enhanced pain perception due to lack of endorphins Signup and view all the answers

Which types of hormones do chromophobe adenomas most commonly secrete?

Prolactin Signup and view all the answers

Study Notes

Hypothalamus

Regulates body homeostasis
Controls endocrine functions, visceral functions, metabolic activities, hunger, thirst, sleep, wakefulness, emotion, sexual function
Produces two groups of hormones:
- Peptides: Travel down to the posterior pituitary through nerve fibers and get stored.
  - Arginine-vasopressin/Antidiuretic hormone (ADH)
  - Oxytocin: Initiates uterine contraction during labor, controls milk ejection from lactating breasts
- Regulatory hormones: Small molecules transported through blood network to the anterior pituitary to stimulate or inhibit secretion of anterior lobe hormones.
  - Releasing hormones (RH): Stimulate hormone release
  - Releasing-hormone inhibitory hormones (RHIH): Inhibit hormone release

Pituitary Gland

Located inside the skull below the brain and above the nasal passages
Connected to the hypothalamus
Considered the “master control gland” because hormones it makes control the levels of hormones made by most other endocrine glands in the body
Consists of two parts:
- Anterior pituitary
- Posterior pituitary

Anterior Pituitary Hormones

Classified by stain reaction:
- Acidophils:
  - Somatotrophs: Secrete growth hormone (GH), a polypeptide hormone
    - Stimulates long bone and soft tissue growth
    - Exerts actions on metabolism (amino acid, fatty acid, glucose)
    - Secretions increased via hypoglycaemia, stress, and exercise
    - Hypothalamus regulates GH release through:
      - Growth hormone releasing hormone (GHRH): Stimulates GH release
      - Somatostatin: Inhibits GH release
    - Systemic control via negative feedback by GH at the hypothalamus
    - GH insufficiency causes short stature (dwarfism); GH excess causes gigantism in children, acromegaly in adults
  - Lactotrophs: Secrete prolactin, a polypeptide hormone
    - Stimulates development and growth of secretory alveoli in breast and milk production
    - Inhibits reproductive system at the level of gonads and pituitary (causes ‘lactational amenorrhoea’)
    - Secretion of prolactin is increased by suckling.
    - Prolactin secretion inhibited by dopamine from hypothalamus
    - Hypersecretion: Can cause galactorrhoea, infertility and amenorrhoea
    - Hyposecretion: Can cause lactation failure
- Basophils:
  - Corticotrophs: Synthesize a large polypeptide [pro-opiomelanocortin (POMC)], which is a precursor of:
    - Adrenocorticotrophic hormone (ACTH; corticotrophin): Stimulates steroid synthesis and secretion from adrenal cortex
      - Maintains adrenal cortical growth
      - Secretion increased by stress
      - Secretion pulsatile with a diurnal rhythm
      - Release is stimulated by corticotrophin releasing hormone (CRH) from hypothalamus
      - Release is inhibited by glucocorticoid negative feedback
      - ACTH excess causes Cushing's disease (excess glucocorticoid secretion); ACTH deficiency causes glucocorticoid deficiency
    - Melanocyte stimulating hormone (MSH): Stimulates skin pigmentation via actions on melanocytes of the epidermis
    - β-lipotrophin: Inactive until rapidly converted to endorphins, neurotransmitters that have opiate-like effects and help control pain
  - Gonadotrophs: Secrete gonadotrophins (follicle stimulating hormone (FSH) and luteinizing hormone (LH)), which act on gonads
    - Gonadotrophins are glycoprotein hormones made of an α and a β subunit; the α subunit is common with that in TSH, the β subunits are specific to LH and FSH
    - Control growth and development of germ cells of gonads
    - Control synthesis and secretion of sex hormones (testosterone, oestrogen and progesterone)
    - LH and FSH release stimulated by gonadotrophin releasing hormone (GnRH) during reproductive life
    - LH and FSH release is inhibited by sex steroids by negative feedback
    - Deficiencies: Cause infertility in adult life and lack of sexual maturation in children
    - Excess: Cause precocious puberty
  - Thyrotrophs: Secrete TSH (thyrotrophin), which acts on the thyroid gland
    - Glycoprotein hormone made of α and β subunits; the β subunit is specific to TSH, the α subunit is shared with LH and FSH
    - TSH acts in the thyroid:
      - Stimulates thyroid hormones (T3 and T4) production
      - Increases iodine uptake by the thyroid (required for thyroid hormone production)
      - Stimulates thyroid growth
    - TSH release stimulated by thyrotrophin releasing hormone (TRH) from the hypothalamus
    - TRH secretion is stimulated by stress via the CNS
    - TSH is released in pulses with a diurnal rhythm
    - TSH release inhibited by T3 & T4 negative feedback
- Chromophobes: Once considered inactive, they do contain secretory granules. Chromophobe adenomas often secrete hormones, particularly prolactin.

Posterior Pituitary Hormones

Two structurally similar peptide hormones:
- Antidiuretic hormone (ADH) also called vasopressin or arginine vasopressin (AVP)
- Oxytocin: Synthesized in the hypothalamus and stored in the posterior pituitary, released into the bloodstream when needed.

Hypopituitarism

Deficiency of pituitary hormone production
Can result from disorders of the hypothalamus, pituitary or surrounding structures
Clinical features usually absent until about 70 per cent of the gland has been destroyed, unless there is associated hyperprolactinaemia, when amenorrhoea and infertility may be early symptoms.
Panhypopituitarism: Involvement of all pituitary hormones
Partial hypopituitarism: Only one or more pituitary hormones involved
Causes: Tumours, infections (tuberculosis, meningitis and syphilis), infiltrations, head injury and etc.
Consequences:
- Growth retardation in children: Due to deficiency of GH
- Secondary hypogonadism: Due to gonadotrophin deficiency, presenting as amenorrhoea, infertility and atrophy of secondary sexual characteristics with loss of axillary and pubic hair and impotence or loss of libido. Puberty is delayed in children.
- Secondary adrenocortical hypofunction (ACTH deficiency): Cortisol is necessary for the maintenance of normal blood pressure. Hypotension may be associated with ACTH deficiency. Cortisol and/or GH deficiency may cause increased insulin sensitivity with fasting hypoglycaemia.
- Secondary hypothyroidism (TSH deficiency): May sometimes be clinically indistinguishable from primary hypothyroidism.
- Prolactin deficiency: Associated with failure to lactate, this may occur after post-partum pituitary infarction (Sheehan’s syndrome). However, in hypopituitarism due to a tumour, plasma prolactin concentrations are often raised and may cause galactorrhoea.

Investigation of Suspected Hypopituitarism

Deficiency of pituitary hormones causes hypofunction of the target endocrine glands.
Investigation aims:
- To confirm the deficiency
- To exclude disease of the target gland
- To test pituitary hormone secretion after maximal stimulation of the gland
Plasma concentrations should be measured:
- LH, FSH and oestradiol (female) or testosterone (male)
- Total or free T4 and TSH
- Prolactin
- Cortisol at 09.00 h, to assess the risk of adrenocortical insufficiency
If the plasma concentration of the target gland hormone is low and the concentration of trophic hormone is raised, investigate the affected target gland.
If the plasma concentrations of both the target gland and trophic hormones are low or low-normal, consider a pituitary stimulation test.
Investigation of the pituitary region using radiological techniques such as CT or MRI scanning may help elucidate a cause of the hypopituitarism.

Combined Pituitary Stimulation Tests

Insulin or glucagon plus TRH and GnRH given as one test is used to evaluate pituitary hormones.

Insulin Stimulation Test

Potentially dangerous and must be done under direct medical supervision.
Indications:
- Assessment of GH in growth deficiency.
- Assessment of ACTH/cortisol reserve.
- Differentiation of Cushing’s syndrome from pseudo-Cushing’s syndrome, for example depression or alcohol excess.
After an overnight fast:
- Insert an indwelling intravenous cannula.
- Take basal samples at time 0 minute for cortisol, GH and glucose
- Inject soluble insulin in a dose sufficient to lower plasma glucose concentrations to less than 2.5 mmol/L and evoke symptomatic hypoglycaemia
- Take blood samples at 30, 45, 60, 90 and 120 minutes after the injections for cortisol, GH and glucose assays
If hypoglycaemia has been adequate, plasma cortisol concentrations should rise by more than 200 nmol/L and exceed 580 nmol/L, and an adequate GH response occurs with an absolute response of greater than 20 mU/L (7 µg/L).

Glucagon Stimulation Test

Useful if the insulin hypoglycaemic test is contraindicated.
Must be carried out in a specialist unit by experienced staff.
Principle: Glucagon stimulates GH and ACTH release probably via a hypothalamic route.
Patients should fast overnight.
Insert an indwelling intravenous cannula.

Hypothalamus

The hypothalamus controls various bodily functions such as hormone production, visceral activity, metabolism, hunger, thirst, sleep, wakefulness, emotion, sexual function, etc.
It releases two hormone groups:
- Posterior Pituitary Hormones: Travel through nerve fibers to the posterior pituitary where they are stored.
  - Arginine-vasopressin (ADH) or antidiuretic hormone
  - Oxytocin: controls milk ejection and uterine contraction
- Anterior Pituitary Hormones: Small molecules or regulatory hormones transported through blood to the anterior pituitary.
  - Releasing hormones (RH) and releasing hormones-inhibitory hormones (RHIH)

Pituitary Gland

Situated beneath the brain and above the nasal passages, it's connected to the hypothalamus.
Hormones released by hypothalamus stimulate production of hormones in the pituitary gland.
Known as the “master control gland” due to its influence on hormone levels in other endocrine glands.
Consists of two parts:
- Anterior Pituitary: Synthesizes and secretes several hormones.
- Posterior Pituitary: Stores and releases hormones produced by the hypothalamus.

Anterior Pituitary Hormones

Cells in the anterior lobe are categorized as acidophils, basophils, and chromophobes:
- Acidophils:
  - Somatotrophs: Secrete growth hormone (GH) which stimulates growth of bones and tissues and influences metabolism.
    - Increased secretion due to hypoglycemia, stress, and exercise.
    - Regulated by growth hormone releasing hormone (GHRH) and somatostatin from the hypothalamus.
    - GH deficiency causes dwarfism; excess GH causes gigantism in children and acromegaly in adults.
  - Lactotrophs: Secrete prolactin which promotes breast development and milk production.
    - Inhibits the reproductive system, causing lactational amenorrhea.
    - Secretion stimulated by suckling.
    - Prolactin release is inhibited by dopamine from the hypothalamus.
    - Prolactin excess causes galactorrhea, infertility, and amenorrhea.
    - Low prolactin causes lactation failure.
- Basophils:
  - Corticotrophs: Synthesize a precursor (POMC) for adrenocorticotrophic hormone (ACTH), melanocyte stimulating hormone (MSH), and β-lipotrophin.
    - ACTH stimulates steroid production and growth in the adrenal cortex.
    - ACTH release is increased by stress and follows a diurnal rhythm.
    - Regulated by corticotrophin releasing hormone (CRH).
    - ACTH excess from pituitary tumors causes Cushing's disease.
    - ACTH deficiency causes glucocorticoid deficiency.
    - MSH stimulates skin pigmentation by influencing melanocytes.
    - β-Lipotrophin is converted to endorphins with opiate-like pain control effects.
  - Gonadotrophs: Secrete gonadotrophins (follicle stimulating hormone (FSH) and luteinizing hormone (LH)).
    - They act on the gonads, control germ cell development, and regulate production of sex hormones (testosterone, estrogen, and progesterone).
    - Release stimulated by gonadotrophin releasing hormone (GnRH) during reproductive life.
    - Inhibited by sex steroid negative feedback.
    - Deficiencies cause infertility in adults and delayed sexual maturation in children.
    - Excess causes precocious (early) puberty.
  - Thyrotrophs: Secrete thyroid stimulating hormone (TSH).
    - Stimulates thyroid hormone (T3 and T4) production, iodine uptake, and thyroid growth.
    - Release is stimulated by thyrotrophin releasing hormone (TRH) from the hypothalamus.
    - TRH release is triggered by stress through the CNS.
    - TSH release follows a diurnal rhythm.
    - Inhibited by T3 & T4 negative feedback.
- Chromophobes: Initially considered inactive but can contain secretory granules. - Chromophobe adenomas often secrete hormones, particularly prolactin.

Posterior Pituitary Hormones

Two peptides (ADH and oxytocin) are synthesized in the hypothalamus and stored in the posterior pituitary:
- Antidiuretic Hormone (ADH)(Vasopressin): Regulates water balance and blood pressure.
- Oxytocin: Promotes milk ejection and uterine contraction.

Hypopituitarism

Syndrome of pituitary hormone deficiency caused by disorders of the hypothalamus, pituitary, or surrounding structures
Symptoms often absent until 70% of the gland is destroyed, unless hyperprolactinaemia is present, which can cause early amenorrhoea and infertility.
Panhypopituitarism: affects all pituitary hormones.
Partial hypopituitarism: involves one or more hormones.
Causes include tumors, infections, infiltrations, head injury, etc.
Consequences:
- Growth retardation (GH deficiency): in children.
- Secondary hypogonadism (gonadotrophin deficiency): Amenorrhoea, infertility, atrophy of secondary sexual characteristics (loss of hair), and impotence or loss of libido.
- Secondary adrenocortical hypofunction (ACTH deficiency): Hypotension and increased insulin sensitivity with fasting hypoglycemia.
- Secondary hypothyroidism (TSH deficiency): Often indistinguishable from primary hypothyroidism.
- Prolactin deficiency: Failure to lactate.

Investigating Hypopituitarism

Measures plasma concentrations of:
- LH, FSH, and oestradiol (women) or testosterone (men)
- Total or free T4 and TSH
- Prolactin
- Cortisol at 09.00 h to assess adrenocortical insufficiency.
Imaging (CT or MRI) to investigate the pituitary area.

Insulin Stimulation Test

Potentially dangerous, requiring medical supervision.
Indications:
- Assessment of GH for growth deficiency.
- Assessment of ACTH/cortisol reserve.
- Differentiating Cushing’s syndrome from pseudo-Cushing’s syndrome (depression, alcohol excess).
Procedure:
- Overnight fasting with an intravenous line inserted.
- Take basal samples at time 0 for cortisol, GH, and glucose.
- Inject insulin to lower glucose levels below 2.5 mmol/L, evoking hypoglycemia.
- Take blood samples at 30, 45, 60, 90, and 120 minutes after injection for cortisol, GH, and glucose assays.
Adequate response:
- Cortisol rise exceeding 200 nmol/L, exceeding 580 nmol/L.
- GH response exceeding 20 mU/L (7 µg/L).

Glucagon Stimulation Test

Used if insulin hypoglycemic test is contraindicated.
Requires specialist unit and experienced staff.
Glucagon stimulates GH and ACTH release, potentially through a hypothalamic route.
Procedure:
- Overnight fasting with an intravenous line inserted.
- Take basal samples at time 0 for cortisol, GH, and glucose.
- Administer glucagon intravenously.
- Take blood samples periodically.
- Evaluate GH and ACTH responses.

Anterior Pituitary Hormones

Acidophils
- Somatotrophs secrete growth hormone (GH), a polypeptide hormone that stimulates long bone and soft tissue growth.
- GH also influences amino acid, fatty acid, and glucose metabolism.
- Increased GH secretion is triggered by hypoglycemia, stress, and exercise.
- Growth hormone-releasing hormone (GHRH) and somatostatin from the hypothalamus regulate GH release.
- GH insufficiency leads to short stature (dwarfism), while excess GH results in gigantism in children and acromegaly in adults.
- Lactotrophs secrete prolactin, a polypeptide hormone that stimulates breast development, growth of secretory alveoli, and milk production.
- Prolactin also inhibits the reproductive system at the level of the gonads and pituitary, causing "lactational amenorrhea" after childbirth.
- Suckling increases prolactin secretion, while dopamine from the hypothalamus inhibits it.
- Hypersecretion of prolactin can cause galactorrhea, infertility, and amenorrhea.
- Hyposecretion of prolactin can cause lactation failure.
Basophils
- Corticotrophs synthesize pro-opiomelanocortin (POMC), a precursor to adrenocorticotrophic hormone (ACTH), melanocyte-stimulating hormone (MSH), and β-lipotrophin.
- ACTH stimulates adrenal cortex steroid synthesis and secretion, maintaining adrenal cortical growth.
- Stress increases ACTH secretion, which follows a pulsatile pattern with a diurnal rhythm.
- Corticotrophin-releasing hormone (CRH) from the hypothalamus stimulates ACTH release.
- Glucocorticoids inhibit ACTH release through negative feedback.
- Excess ACTH from pituitary tumors causes Cushing's disease, while ACTH deficiency leads to glucocorticoid deficiency.
- MSH, also cleaved from POMC, stimulates skin pigmentation by increasing melanin production in melanocytes of the epidermis.
- β-lipotrophin is inactive until converted to endorphins, neurotransmitters with opiate-like effects, controlling pain.
- Gonadotrophs secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH), glycoprotein hormones that act on the gonads.
- Gonadotrophin-releasing hormone (GnRH) stimulates LH and FSH release during reproductive life.
- Sex steroids inhibit LH and FSH release through negative feedback.
- Deficiencies in LH and FSH cause infertility in adults and lack of sexual maturation in children.
- Excess LH and FSH secretion leads to precocious puberty.
- Thyrotrophs secrete thyroid-stimulating hormone (TSH), a glycoprotein hormone made up of α and β subunits, with the β subunit specific to TSH.
- TSH stimulates thyroid hormone (T3 and T4) production, increases iodine uptake by the thyroid, and promotes thyroid growth.
- Thyrotropin-releasing hormone (TRH) from the hypothalamus stimulates TSH release.
- Stress via the CNS stimulates TRH secretion.
- TSH release follows a pulsatile pattern with a diurnal rhythm.
- T3 and T4 inhibit TSH release through negative feedback.
Chromophobes
- These cells were previously thought to be inactive, but they contain secretory granules.
- Chromophobe adenomas often secrete hormones, particularly prolactin.

Posterior Pituitary Hormones

Antidiuretic hormone (ADH), also called vasopressin or arginine vasopressin (AVP), and oxytocin are synthesized in the hypothalamus and transported to the pituitary by neurophysins.
Both hormones are stored and released independently from the posterior pituitary gland under hypothalamic control.
Antidiuretic hormone (ADH) is a peptide of nine amino acids.
ADH enhances water reabsorption from the collecting ducts of the kidney, regulating plasma osmolality.
Increased plasma osmolality stimulates hypothalamic osmoreceptors, leading to ADH secretion.
Defective ADH production or action causes diabetes insipidus (hypothalamic or cranial, and renal or nephrogenic, respectively).
Oxytocin controls milk ejection during lactation and may contribute to initiating uterine contractions, although normal labor can proceed without it.
Oxytocin can be used therapeutically to induce labor.

Control of Pituitary Hormone Secretion

Extrahypothalamic neural stimuli can modify or override other control mechanisms.
Physical or emotional stress and mental illness can resemble and even trigger endocrine disorders.
Feedback control is mediated by circulating target cell hormone concentrations, with rising concentrations typically suppressing trophic hormone secretion.
This negative feedback can directly suppress hypothalamic hormone secretion or modify its effect on pituitary cells (long feedback loop).
Increasing pituitary hormone concentrations can suppress hypothalamic hormone secretion in a short feedback loop.
Hypothalamic and pituitary hormones are released intermittently, either in pulses or in a regular circadian rhythm.
Drugs can stimulate or block neurotransmitter action, such as certain neuroleptic drugs that interfere with dopamine action.
This can reduce GH secretion (diminished effect of releasing factor) and increase prolactin secretion (reduced inhibition).
Bromocriptine, with a dopamine-like action, and levodopa, converted to dopamine, decrease prolactin secretion.

Hypopituitarism

Hypopituitarism is a syndrome of deficient pituitary hormone production caused by disorders of the hypothalamus, pituitary, or surrounding structures.
Clinical features of deficiency usually remain absent until about 70 percent of the gland is destroyed, unless hyperprolactinemia is present, in which case amenorrhea and infertility may be early symptoms.
Panhypopituitarism involves all pituitary hormones, while partial hypopituitarism affects one or more hormones.
Although isolated hormone deficiency, particularly of GH, may occur, multiple hormones are commonly involved.
Causes of hypopituitarism include tumors, infections (tuberculosis, meningitis, syphilis), infiltrations, head injury, and other factors.

Consequences of Pituitary Hormone Deficiencies

Progressive pituitary damage typically presents with evidence of gonadotropin and GH deficiencies.
Plasma ACTH and/or TSH concentrations may remain normal or become deficient months or years later.
Clinical and biochemical consequences of target gland failure include:
- Growth retardation in children due to GH deficiency.
- Secondary hypogonadism due to gonadotropin deficiency, manifesting as amenorrhea, infertility, atrophy of secondary sexual characteristics, loss of axillary and pubic hair, impotence, and loss of libido. Puberty is delayed in children.
- Secondary adrenocortical hypofunction (ACTH deficiency), leading to hypotension. Cortisol or GH deficiency can cause increased insulin sensitivity with fasting hypoglycemia.
- Secondary hypothyroidism (TSH deficiency), sometimes clinically indistinguishable from primary hypothyroidism.
- Prolactin deficiency associated with failure to lactate, which can occur after postpartum pituitary infarction (Sheehan's syndrome). However, in hypopituitarism due to a tumor, plasma prolactin concentrations are often elevated and may cause galactorrhea.

Investigation of Suspected Hypopituitarism

Pituitary hormone deficiency causes hypofunction of the target endocrine glands.
Investigation aims to:
- Confirm deficiency.
- Exclude target gland disease.
- Test pituitary hormone secretion after maximal stimulation of the gland.
Measurement of plasma concentrations of:
- LH, FSH, and estradiol (female) or testosterone (male).
- Total or free T4 and TSH.
- Prolactin.
- Cortisol at 09:00 h to assess the risk of adrenocortical insufficiency.
If plasma concentration of the target gland hormone is low and the concentration of the trophic hormone is elevated, investigate the affected target gland.
If the plasma concentration of both the target gland and trophic hormones are low or low-normal, consider a pituitary stimulation test.
Radiological techniques such as CT or MRI scans can help determine the cause of hypopituitarism.
Combined pituitary stimulation tests (insulin or glucagon plus TRH and GnRH given as a single test) can be used to evaluate pituitary hormones.

Insulin Stimulation Test

This potentially dangerous test must be performed under direct medical supervision.
Indications for the insulin stimulation test:
- Assessment of GH in growth deficiency.
- Assessment of ACTH/cortisol reserve.
- Differentiation of Cushing's syndrome from pseudo-Cushing's syndrome (e.g., depression or alcohol excess).
After an overnight fast, an intravenous cannula is inserted.
Basal samples are taken at time 0 for cortisol, GH, and glucose.
Soluble insulin is injected in a dose sufficient to lower plasma glucose concentrations to less than 2.5 mmol/L, inducing symptomatic hypoglycemia.
Blood samples are taken at 30, 45, 60, 90, and 120 minutes after injections for cortisol, GH, and glucose assays.
If hypoglycemia is adequate, plasma cortisol concentrations should rise by more than 200 nmol/L and exceed 580 nmol/L, and an adequate GH response occurs with an absolute response greater than 20 mU/L (7 µg/L).

Glucagon Stimulation Test

This test is useful if the insulin hypoglycemic test is contraindicated.
However, it must be performed in a specialist unit by experienced staff.
Glucagon stimulates GH and ACTH release, likely through a hypothalamic route.
Patients should fast overnight.
An intravenous cannula is inserted.

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This quiz covers the critical functions of the hypothalamus and pituitary gland within the endocrine system. It delves into how they regulate body homeostasis, hormone production, and various physiological functions such as hunger, thirst, and emotions. Test your understanding of these essential components of human biology.