Hormones: Types, Sources, and Mechanisms

Hormones

• Hormones are chemical messengers secreted into the bloodstream by endocrine cells.
• These messengers affect cells possessing specific receptors.
• Hormones are derived from either amino acids or cholesterol.

Sources of Hormones

• Hormones originate from endocrine glands like the pituitary, thyroid, parathyroid, adrenal, pineal, and thymus.
• The pancreas, ovaries or testes, hypothalamus, skin, heart, stomach, liver, kidney, and small intestine also produce hormones.

Control of Hormone Release

• Hormone release is regulated by the nervous system signals, other hormones, and chemical changes in the blood.
• Negative feedback is the most common regulatory mechanism.

Hormone Transport

• Water-soluble hormones circulate freely in the blood plasma.
• Lipid-soluble hormones bind to transport proteins
• Only unbound hormones can diffuse out of capillaries and bind to receptors.

Mechanisms of Hormone Action

• Lipid-soluble hormones diffuse into cells, bind to intracellular receptors, and alter gene expression.
• Water-soluble hormones bind to membrane receptors, activate 2nd messenger systems, and amplify the original signal.

Hormone Interactions

• Permissive effects occur when one hormone enhances a target organ's response to a second, later hormone, such as estrogen preparing the uterus for progesterone.
• Synergistic effects happen when hormones act together to produce a greater effect, for example, FSH and testosterone for sperm production.
• Antagonistic effects involve one hormone opposing the action of another, like insulin lowering blood glucose while glucagon raises it.

Pituitary Gland

• The pituitary is a pea-shaped structure extending from the hypothalamus.

Anterior Pituitary Hormones

• The anterior pituitary lobe synthesizes and secretes multiple hormones.
• Growth hormone (GH) stimulates growth.
• Thyroid-stimulating hormone (TSH) stimulates the thyroid gland.
• Adrenocorticotropic hormone (ACTH) stimulates the adrenal cortex.
• Follicle-stimulating hormone (FSH) stimulates follicle growth or sperm production.
• Luteinizing hormone (LH) triggers ovulation and testosterone production.
• Prolactin (PRL) stimulates milk production.
• The hypothalamus controls all of these hormones through releasing and inhibiting hormones.

Posterior Pituitary Hormones

• The posterior pituitary lobe stores and releases hormones produced by the hypothalamus.
• Oxytocin stimulates uterine contractions and milk ejection.
• Antidiuretic hormone (ADH) promotes water retention by the kidneys.

Thyroid Gland

• The thyroid gland in the neck produces thyroid hormones (T3 and T4) that regulates metabolism.
• T3 and T4 synthesis, which requires iodine, are released in response to TSH from the pituitary.

Parathyroid Glands

• The parathyroid glands, located on the thyroid gland's posterior surface, produce parathyroid hormone (PTH).
• PTH regulates calcium levels in the blood.
• PTH increases blood $Ca^{2+}$ by stimulating osteoclasts and inhibiting osteoblasts.

Adrenal Glands

• The adrenal glands sit atop the kidneys and consist of two parts.
• The adrenal cortex produces corticosteroids regulating metabolism, stress response, and electrolyte balance.
• Cortisol, a stress hormone, is released.
• ACTH from pituitary stimulates release.
• Cortisol promotes breakdown of fat and protein and suppresses the immune system.
• Aldosterone causes kidneys to retain sodium.
• The adrenal medulla produces epinephrine and norepinephrine (catecholamines).
• The "fight or flight" response is stimulated by sympathetic nervous system.

Pancreas

• The pancreas, in the abdomen, has endocrine and exocrine functions.
• Insulin lowers blood glucose levels/ stimulates glucose uptake by cells..
• Glucagon raises blood glucose levels by stimulating glycogen breakdown in the liver.
• Diabetes Mellitus is characterized by the inability to produce or respond to insulin.

Pineal Gland

• The pineal gland, located in the brain, produces melatonin.
• Melatonin regulates sleep-wake cycles.

Thymus

• The thymus located in the chest produce hormones that regulate immune function.
• Thymosins stimulate maturation of T-lymphocytes

Ovaries and Testes

• Both ovaries and testes are the sites of production of sex hormones that regulate reproduction and development of secondary sex characteristics.
• Estrogen and progesterone are produced by ovaries.
• Testes produce testosterone..

Stressor

• Any stimulus that produces a stress response.

General Adaptation Syndrome (GAS)

• GAS is a three-stage reaction to stress:

1. Alarm reaction: "Fight or flight" response mediated by the sympathetic nervous system and adrenal medulla.
2. Resistance reaction: Long-term response mediated by the adrenal cortex (cortisol).
3. Exhaustion: Depletion of body resources leading to sickness and death.

Effects of Stress

• Prolonged exposure to high levels of cortisol can suppress the immune system, increase the risk of infection, and delay wound healing.
• Stress can also contribute to heart disease, high blood pressure, and other health problems.

Roots

• If $f(c) = 0$, then $c$ is a root (or zero) of the function $f(x)$.
• Roots Theorem:
  • $x = c$ is a root of $f(x)$
  • $x = c$ is a solution of the equation $f(x) = 0$
  • $(x - c)$ is a factor of $f(x)$
  • $x = c$ is an x-intercept of $f(x)$

Factor Theorem

• $f(x)$ has a factor $(x - k)$ if and only if $f(k) = 0$

Rational Root Theorem

• Every rational root of $f(x) = a_n x^n + a_{n-1} x^{n-1} +... + a_1 x + a_0= 0$ is of the form $\frac{p}{q}$ where:
  • p is a factor of the constant coefficient $a_0$
  • q is a factor of the leading coefficient $a_n$

Diffie-Hellman Key Exchange

• Public Parameters: Prime $p$, generator $g$ of $\mathbb{Z}_p^*$ (i.e., $g$ is a number s.t. ${g^0, g^1, g^2, \ldots, g^{p-2}}$ are all distinct modulo $p$).
• Alice chooses random $a \in {1, \ldots, p-1}$, sends $g^a \mod p$ to Bob
• Bob chooses random $b \in {1, \ldots, p-1}$, sends $g^b \mod p$ to Alice
• Alice computes $(g^b)^a = g^{ab} \mod p$
• Bob computes $(g^a)^b = g^{ab} \mod p$
• Shared secret: $g^{ab} \mod p$
• No authentication.
• Mallory chooses random $m_1, m_2 \in {1, \ldots, p-1}$. Mallory sends $g^{m_1} \mod p$ to Alice and $g^{m_2} \mod p$ to Bob. Alice computes $(g^{m_1})^a = g^{am_1} \mod p$
• Bob computes $(g^{m_2})^b = g^{bm_2} \mod p$
• Mallory computes:
  • $(g^a)^{m_1} = g^{am_1} \mod p$
  • $(g^b)^{m_2} = g^{bm_2} \mod p$

RSA

• Alice has public key $pk$ and secret key $sk$ Bob sends message $m$ to Alice and computes $c \leftarrow Enc(pk, m)$. Bob sends $c$ to Alice and she computes $m \leftarrow Dec(sk, c)$
• Public parameters: integer $N$, integers $e, d$Public key: $(N, e)$
• Secret key: $d$
• Encryption: $Enc((N, e), m) = m^e \mod N$
• Decryption: $Dec(d, c) = c^d \mod N$
• How to choose $N, e, d$?
  1. Choose two large primes $p$ and $q$.
  2. Let $N = pq$.
  3. Choose integer $e$ s.t. $gcd(e, (p-1)(q-1)) = 1$.
  4. Compute $d = e^{-1} \mod (p-1)(q-1)$. I.e., $de = 1 \mod (p-1)(q-1)$.
• $m^{ed} = m \mod N$ for all $m \in \mathbb{Z}_N^*$.
• ed = 1 mod (p-1)(q-1) ⇒ ed = 1 + k(p-1)(q-1) for some integer k.
• Then $m^{ed} = 0 \mod p$ and $m^{ed} = m \mod q$ Implementation details
  • Choose a random number and check if it is prime.
  • Primality testing algorithms (e.g., Miller-Rabin primality test)
• How to choose $e$?
  • Choose a random number and check if $gcd(e, (p-1)(q-1)) = 1$.
• How to compute $d = e^{-1} \mod (p-1)(q-1)$?
  • Use the extended Euclidean algorithm.
• How to compute $m^e \mod N$?
  • Use repeated squaring.
• RSA is still considered secure if $N$ is large enough (e.g., 2048 bits).

Explore hormones as chemical messengers secreted by endocrine cells, their origins from various glands and organs, and the regulatory mechanisms governing their release. Learn about hormone transport in the bloodstream and the diverse mechanisms through which hormones exert their effects on target cells.