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Overview

🌳 Concept tree

Lesson 1→Endocrine Glands, The Pituitary, Thyroid and Parathyroid Glands

├── Control of body functions

├── What is a hormone?
├── Discovery of animal hormones — Starling (1905)

├── Plant hormones — Jensen (1913)

├── How scientists found out what hormones do

├── Characteristics of hormones

├── Types of glands in man

├── Position and structure

├── Hormones of the adenohypophysis (anterior lobe)
├── Hormones of the neurohypophysis (posterior lobe)

├── The thyroid gland

├── Diseases of the thyroid (due to hypo- or hypersecretion of thyroxine)

└── The parathyroid glands

Lesson 1: Endocrine Glands, The Pituitary, Thyroid and Parathyroid Glands · 1 / 15

Control of body functions

All the activities of the body are controlled by two systems the nervous system (fast, short-lived, electrical and chemical messages through nerves) and the endocrine (hormonal) system (slower, longer-lasting chemical messages through blood).
The two systems work together; the hypothalamus of the brain is the link between them.

The endocrine glands are ductless glands they have no tubes, and they pour their secretions (the hormones) directly into the blood stream.
Any increase (hypersecretion) or decrease (hyposecretion) in the amount of a hormone disturbs the functions it controls and causes the characteristic symptoms of a disease.

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What is a hormone?

A hormone is a chemical substance that is made and secreted by an endocrine gland, carried by the blood to another organ (the target organ), where it affects the function and growth of that organ.
Most of the actions of hormones are in the form of stimulation of other glands or organs.
(The word hormone is Greek and means "to activate" or "to excite".)

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Discovery of animal hormones — Starling (1905)

Starling and Bayliss studied how the pancreas starts to secrete pancreatic juice:

The pancreas begins to secrete pancreatic juice soon after food reaches the duodenum, even after the nerves supplying the pancreas have been cut.
So he concluded that there must be a non-nervous stimulus.
He then discovered that the mucous membrane lining the duodenum secretes a chemical substance (secretin) that passes into the blood and stimulates the pancreas to secrete pancreatic juice.
He named these substances hormones ("activators").

Logic of the experiment→cut nerve → secretion still occurs → so another route (blood) must carry the message; extract from duodenal lining injected into blood → pancreas secretes → the chemical messenger exists.

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Plant hormones — Jensen (1913)

B.
Jensen explained phototropism (bending of the growing tip towards light) by auxins.
He showed that the link between the receptor (the tip that perceives the light) and the region of curvature (the growing region below it) is a chemical substance — an auxin such as indole acetic acid (IAA).
(Jensen showed that a tip cut and replaced on a decapitated coleoptile, with a thin separating block of gelatin that lets chemicals pass but not cells, still allowed bending.)
Plants have no special glands for hormones; auxins are made by the tips of coleoptiles and by buds and affect other parts of the plant.
Functions of auxins:

They organise the development and differentiation of tissues; they cause cell elongation (growth).
They control flowering, fruit formation and ripening (e.g. the ovary produces auxin that makes it develop into a fruit — see Chapter 3 on parthenocarpy).
in a shoot the auxin moves to the shaded side, where it speeds up cell elongation, so the shoot bends toward the light.

Lesson 1: Endocrine Glands, The Pituitary, Thyroid and Parathyroid Glands · 5 / 15

How scientists found out what hormones do

By studying the symptoms produced when an endocrine gland is enlarged (over-active) or removed in man and animals (gland removal and gland transplants).
By studying the chemical structure of extracts of the glands, and the effects of injecting the extracts on different vital activities.

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Characteristics of hormones

They are organic substances; some are proteins (insulin, growth hormone), some amino acids (thyroxine, adrenaline), some steroids (lipid derivatives: sex hormones, cortisone, aldosterone).
They are secreted in very small amounts (micrograms; 1 µg = 1/1000 mg) and are effective in tiny amounts.
They are carried by the blood and act on target organs that are often far from the gland.
They are destroyed after acting (in the liver or kidney), so their action is temporary and must be renewed.
They are not species specific in most cases (insulin from a pig can treat a diabetic person), though this is not always so.

General functions of hormones:

maintain the balance of the internal environment (homeostasis);

control body growth;

bring about sexual maturity and reproduction;

regulate metabolism (utilisation of food);

affect human behaviour, emotional and intellectual development.

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Types of glands in man

Type	Structure	Secretion goes	Examples
Exocrine	Secretory cells + a duct (or system of ducts)	Through ducts to a cavity in the body or to outside	Salivary glands gastric glands sweat glands liver (bile) pancreas (juice)
Endocrine	Ductless	Directly into blood	Pituitary thyroid parathyroids adrenals gonads (hormone part)
Mixed	Part exocrine, part endocrine	Both	Pancreas, testes, ovaries (gametes + hormones)

The pancreas is a mixed gland its acini make pancreatic juice delivered through the pancreatic duct to the duodenum (exocrine), while the islets of Langerhans make insulin and glucagon released into the blood (endocrine).
The testes and ovaries are mixed as they make gametes (exocrine-like, released through ducts) and sex hormones (endocrine).

✍️ Worked examples

Worked example 1.
A researcher finds a gland whose secretion collects in a tube leading to the small intestine, and also finds clusters of cells within the same gland without tubes, near capillaries.
What kind of gland, and which part makes the hormone?
A mixed gland (pancreas); the clusters (islets of Langerhans) make the hormones.
Worked example 2.
Why can a hormone injected into the blood only affect certain organs?
Only the cells of the target organ have receptors that recognise that hormone.

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Position and structure

The pituitary gland (hypophysis) is a small gland below the brain, connected to the hypothalamus by a stalk (infundibulum).
It is called the master gland because it controls the function and secretion of most of the other endocrine glands (thyroid, adrenal cortex, gonads), and because the hypothalamus controls its own secretion — hormones of the hypothalamus regulate the pituitary.
It has two parts:

Adenohypophysis(glandular part): the anterior lobe and middle lobe.

Neurohypophysisthe posterior lobe plus the infundibulum (nervous part).

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Hormones of the adenohypophysis (anterior lobe)

Growth hormone (GH, somatotrophin). Controls metabolism, especially protein synthesis, and thus controls the physical growth of the body, mainly of bone and muscle.

Hyposecretion in childhood → dwarfism(small but normal proportions and normal mind).

Hypersecretion in childhood → gigantism(very tall).

Hypersecretion in adults → acromegalyafter the long bones have stopped growing, the bones of the extremities (hands, feet, fingers, jaw, and the face bones) thicken and enlarge.

2. Pituitary trophinstropic hormones that affect the activity and secretion of other glands:

Comparison aspect	Main idea	Keywords
Thyrotrophin (TSH, thyroid-stimulating hormone)	stimulates the thyroid gland to make and release thyroxine	stimulatesglandmakerelease
Adrenocorticotrophic hormone (ACTH)	stimulates the adrenal cortex	stimulatesadrenalcortex
Gonadotrophic hormones	affect the gonads (ovaries and testes): Follicle-stimulating hormone (FSH): in females stimulates the growth of the ovarian follicles up to the Graafian follicle in males stimulates the seminiferous tubules to make sperms. Luteinizing hormone (LH): in females causes ovulation and the formation of the corpus luteum in males stimulates the interstitial cells of the testes to secrete testosterone. These two are necessary for sexual maturity. 3. Prolactin: stimulates the mammary glands to produce milk	affectgonadsovariestestes

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Hormones of the neurohypophysis (posterior lobe)

These hormones are produced by neurosecretory cells in the hypothalamus, travel down the nerve fibres through the infundibulum to the posterior lobe, are stored in the nerve endings, and are released into the blood when needed.

Comparison aspect	Main idea	Keywords
Antidiuretic hormone (ADH, vasopressin)	increases the reabsorption of water in the kidney tubules (nephron) so urine volume falls and urine becomes concentrated it also raises blood pressure (constricts blood vessels). Deficiency causes diabetes insipidus — large volumes of dilute urine and great thirst (this is a different disease from diabetes mellitus)	increasesreabsorptionwaterkidney
Oxytocin	causes contraction of the uterine muscles during delivery (labour). Doctors use it to induce or speed up birth it also stimulates the release (ejection) of milk from the mammary glands in response to suckling	causescontractionuterinemuscles

A note on the "extract of the posterior lobe of the cow’s pituitary" given in some cases of delivery: it contains oxytocin that makes the uterus contract strongly to help delivery.

Worked example 3 (growth disorder diagnosis).→A 12-year-old boy is 2.1 m tall with normal proportions; his hand bones are still growing and his growth plates are open. Which hormone and which disorder? Hypersecretion of GH in childhood → gigantism. If a 40-year-old develops enlarged hands, feet, lower jaw and face bones, but not height: acromegaly.

✍️ Worked examples

Worked example 4.
A woman is given an injection during labour and the contractions become stronger.
Which hormone and from which gland?
Oxytocin, posterior pituitary (neurohypophysis; made in the hypothalamus).

Lesson 1: Endocrine Glands, The Pituitary, Thyroid and Parathyroid Glands · 11 / 15

The thyroid gland

Position:

in the neck in front of, and in close contact with, the trachea.
It is slightly reddish, consisting of two lobes joined by a narrow isthmus, surrounded by connective tissue; it is a follicular gland (its cells form follicles that store the hormone).
Hormone: thyroxine (amino-acid hormone). Iodine is essential for its formation.
Effects of thyroxine:

Stimulates physical and mental growth and development.
it raises oxidation of food and heat production.
Increases the absorption of monosaccharides from the intestine.
Keeps the skin and hair healthy.
Thyroxine production is controlled by TSH from the pituitary; high thyroxine in the blood inhibits TSH secretion (negative feedback).

Calcitonin→the thyroid also secretes calcitonin, which lowers blood calcium and prevents calcium from being withdrawn from the bones (stimulates deposition in the bones).

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Diseases of the thyroid (due to hypo- or hypersecretion of thyroxine)

A. Hypothyroidism (low thyroxine)

Simple goitre.→Caused by iodine deficiency in food, water and air. Low thyroxine → the pituitary secretes more TSH → the gland is stimulated and enlarges, but still cannot make enough hormone. Treatment: add iodine to the diet (iodised salt, seafood).
If not treated, complications arise:

Cretinism: severe thyroxine deficiency in childhood → retarded physical and mental growth, large head, short stature and short neck, permanent mental retardation, delayed sexual maturity.
Myxoedema: severe deficiency in adults → dry skin, hair loss, reduced mental and physical activity, weight gain/obesity, low BMR, intolerance to cold, slow heart rate, easy fatigue. Treated by regular medical care and by giving thyroxine or gland extract.

B. Hyperthyroidism (high thyroxine)

Exophthalmic goitre (Graves’ disease).→Hypersecretion of thyroxine → enlargement of the gland and the front of the neck, protrusion of the eyeballs, increased oxidation of food and BMR, weight loss despite good appetite, rapid heart beat, sweating, nervous irritability, tremor, heat intolerance. Treatment: surgical removal of part of the gland, or drugs (or radioactive iodine) that suppress the gland.

Point	Simple goitre	Exophthalmic goitre
Cause	Iodine deficiency → low thyroxine	Over-secretion of thyroxine
Gland	Enlarged	Enlarged
Eyes	Normal	Protruding
BMR and weight	Low BMR, weight gain	High BMR, weight loss
Treatment	Iodine supplement	Remove part of the gland / anti-thyroid drugs

✍️ Worked examples

Worked example 5.
A girl living far from the sea has swelling at the front of the neck, feels cold, is sluggish and gaining weight.
Diagnosis simple goitre (hypothyroidism) from iodine deficiency; treat with iodised salt.
Why is the gland enlarged?
Because low thyroxine removes feedback inhibition, so TSH rises and stimulates the gland to grow.
Worked example 6.
A 30-year-old woman loses weight although she eats well, is nervous and her eyes are prominent.
Diagnosis hyperthyroidism (exophthalmic goitre).

Lesson 1: Endocrine Glands, The Pituitary, Thyroid and Parathyroid Glands · 13 / 15

The parathyroid glands

Comparison aspect	Main idea	Keywords
•	Position	Position
•	four small separate glands embedded in the back of the thyroid gland two on each side	foursmallseparateglands
Hormone: parathormone (PTH).	Secreted when blood calcium falls below normal	Secretedbloodcalciumfalls
•	It raises blood calcium by removing calcium from the bones increasing absorption of calcium in the intestine and reabsorption in the kidneys	raisesbloodcalciumremoving
Parathormone and calcitonin are antagonistic	and together keep blood calcium within normal levels (important for nerve and muscle activity blood clotting and strong bones)	togetherkeepbloodcalcium
Hypersecretion (hyperparathyroidism)	blood calcium rises because the calcium comes mainly from the bones the bones become soft and fragile liable to bend and fracture kidney stones may form	bloodcalciumrisesbecause
Hyposecretion (hypoparathyroidism)	blood calcium falls → painful convulsions and muscle spasms (tetany) and increased excitability of the nervous system so the person gets angry at the slightest cause	bloodcalciumfallspainful
Worked example 7.	After thyroid surgery in the parathyroids were accidentally removed a patient has painful muscle spasms. Why? No parathormone → blood calcium falls → nerves and muscles become over-excitable → tetany. Treatment: calcium and vitamin D	Afterthyroidsurgeryparathyroids

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Part 15

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🔍 In-Depth Explanations, Deductions & Multi-Book Insights:

DABOUR HUB ACADEMY • EGYPTIAN HIGH SCHOOL (THANAWEYA AMMA)
EXPLANATION Lesson 1: Endocrine Glands, The Pituitary, Thyroid and Parathyroid Glands
Course Biology (Senior 3) | Chapter 2 – Hormonal Coordination in Living Organisms | Official Ministerial Syllabus 2026/2027
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1. Academic Lesson Overview & Pedagogical Objectives

Hormones are chemical regulators secreted directly into blood by ductless glands.
This lesson explores the master pituitary gland (adenohypophysis and neurohypophysis), the metabolic thyroid gland (Thyroxine & Calcitonin), and calcium homeostasis parathyroids.

2. Hierarchy Classification Tree (Cognitive Concept Map)

Below is the hierarchical structural tree organizing the conceptual core of this lesson:

The Endocrine System Hierarchy

├── 1. Glandular Classifications: Exocrine (ducted)
Endocrine (ductless)
Mixed (Pancreas
Gonads)

├── 2. Pituitary Gland (The Master Gland)

│ ├── Adenohypophysis (Anterior)GH, TSH, ACTH, FSH, LH, Prolactin

│ └── Neurohypophysis (Posterior)ADH (Vasopressin), Oxytocin

├── 3. Thyroid Gland

│ ├── ThyroxineBasal metabolic rate, mental & physical growth (Goiter disorders)

│ └── CalcitoninLowers blood calcium, deposits Ca2+ into bones

└── 4. Parathyroid Glands

└── Parathormone (PTH)→Raises blood calcium by bone resorption and renal reabsorption

3. The Master Teacher's Blackboard & Exam Rules

Comparison aspect	Main idea	Keywords
•	Extracted high-yield rules golden equations and trap warnings from top Egyptian teachers	Extractedhighyieldrules
• RULE 1	Calcium Antagonism: Calcitonin (from Thyroid) LOWERS blood Ca2+ Parathormone (from Parathyroids) RAISES blood Ca2+	CalciumAntagonismCalcitoninThyroid
• RULE 2	ADH has a dual action: increases water reabsorption in renal tubules (lowers urine volume) and constricts blood vessels (elevates blood pressure)	dualactionincreaseswater
• RULE 3	Growth Hormone (GH) disorders: Deficiency in childhood = Dwarfism Hypersecretion in childhood = Gigantism Hypersecretion in adults = Acromegaly	GrowthHormonedisordersDeficiency
• TRAP	Simple goiter is caused by iodine deficiency Exophthalmic goiter is caused by hyperthyroidism (high metabolic rate weight loss bulging eyes)	Simplegoitercausediodine

Lesson 1: Endocrine Glands, The Pituitary, Thyroid and Parathyroid Glands · 15 / 15

Curriculum

Biology & Geology

Chapter 1 - Support and Movement in Living Organisms

Chapter 2 - Hormonal Coordination in Living Organisms

Chapter 3 - Reproduction in Living Organisms

Chapter 4 - Immunity in Living Organisms

Chapter 5 - Molecular Biology - DNA Structure and Function

Chapter 6 - Molecular Biology - RNA, Protein Synthesis and Genetic Engineering

Chapter 7 - Geology, Earth Sciences and Ecology

Lesson 1: Endocrine Glands, The Pituitary, Thyroid and Parathyroid Glands

🌳 Concept tree

├── Control of body functions

├── Plant hormones — Jensen (1913)

├── How scientists found out what hormones do

├── Characteristics of hormones

├── Types of glands in man

├── Position and structure

├── The thyroid gland

└── The parathyroid glands

control body growth;

bring about sexual maturity and reproduction;

regulate metabolism (utilisation of food);

✍️ Worked examples

✍️ Worked examples

✍️ Worked examples

🔍 In-Depth Explanations, Deductions & Multi-Book Insights:

1. Academic Lesson Overview & Pedagogical Objectives

2. Hierarchy Classification Tree (Cognitive Concept Map)

The Endocrine System Hierarchy

└── 4. Parathyroid Glands

3. The Master Teacher's Blackboard & Exam Rules

Well done! You finished this lesson