Immune & Endocrine Systems – Cell-Mediated Immunity and Endocrine Foundations

Flashcards cover cell-mediated immunity concepts (MHC, T-cell types, transplant rejection, HIV) and foundational endocrine topics (gland types, hormone classes, transport, action, hypothalamus–pituitary relationships).

What are the two major branches of adaptive immunity?

Humoral immunity (antibody-mediated, B cells) and cell-mediated immunity (T cells acting on infected or abnormal cells).

Which class of MHC is found on all nucleated cells and presents to cytotoxic T cells?

MHC class I.

Which class of MHC is restricted to professional antigen-presenting cells and interacts with helper T cells?

MHC class II.

Why are MHC proteins critical in organ transplantation?

Genetic differences in donor MHC can be recognized as foreign by recipient T cells, triggering graft rejection.

What is the primary effector cell that destroys mismatched donor tissue?

Cytotoxic (CD8⁺) T cells.

List two clinical strategies to reduce transplant rejection risk.

Use closely related donors (similar MHC) and perform genotype matching through donor registries.

Role of helper (CD4⁺) T cells in immunity

They bind antigen–MHC II complexes, secrete cytokines, activate cytotoxic T cells, B cells, macrophages, and amplify immune responses.

What cytokine effect does a helper T cell have on a nearby B cell?

Stimulates clonal expansion and differentiation into antibody-secreting plasma cells.

How do cytotoxic T cells kill infected cells?

Release perforin and granzymes that create membrane pores and induce apoptosis.

Function of regulatory (Treg) T cells

Maintain tolerance to self-antigens, suppress overactive T and helper cells, and prevent autoimmunity.

Which immune cells are the primary targets of HIV?

Helper (CD4⁺) T cells.

Why does loss of helper T cells lead to AIDS?

Because helper T cells coordinate both humoral and cell-mediated immunity; their destruction cripples immune responses.

Define endocrine gland.

A gland whose cells secrete hormones directly into the bloodstream.

Define exocrine gland.

A gland that releases products through ducts onto an epithelial surface or into a body cavity.

Key structural difference between endocrine and exocrine secretion

Endocrine uses blood capillaries; exocrine uses epithelial ducts.

Example of an organ with both endocrine and exocrine functions

Pancreas – islets (endocrine: insulin, glucagon) and acinar cells (exocrine: digestive enzymes).

Two major body systems that provide long-distance communication

Nervous system and endocrine system.

Relative speed and specificity: nervous vs endocrine communication

Nervous: very fast, highly addressed to single cells; Endocrine: slower, broadcast to many cells.

Why are hormones effective at very low concentrations?

Signal amplification – one hormone can trigger cascades that produce millions of intracellular effectors.

What determines whether a hormone affects a particular cell?

Presence of a specific receptor for that hormone on or in the cell.

Define neurosecretory (neuroendocrine) cell.

A neuron-like cell that conducts action potentials but releases hormones at its axon terminals into blood.

Name the three chemical classes of hormones.

Steroids, monoamines, and peptides/proteins.

Give two examples of steroid hormones.

Testosterone and cortisol.

Give two examples of monoamine hormones.

Epinephrine and thyroid hormone (T4).

Give two examples of peptide/protein hormones.

Insulin and oxytocin.

Why is thyroid hormone (T4) chemically unusual?

Although a monoamine, it is hydrophobic and travels in blood bound to transport proteins like steroids.

Transport of hydrophilic hormones (peptides/most monoamines) in blood

They dissolve freely in plasma; no carrier needed.

Transport of hydrophobic hormones (steroids & T4) in blood

Bound to plasma transport proteins (e.g., albumin, globulins) which extend their half-life.

Where are receptors for steroids typically located?

Inside target cells, often in the nucleus or cytoplasm.

Primary cellular action pathway for steroid hormones

Bind intracellular receptor → gene activation → mRNA synthesis → new protein production.

Where are receptors for peptide hormones located?

On the cell membrane surface.

Primary cellular action pathway for peptide/monoamine hormones

Bind membrane receptor → activate second-messenger cascades (e.g., cAMP) → modify existing proteins.

Explain why steroid actions show a "lag time".

They require transcription and translation before new proteins alter cell function.

Explain why peptide hormone responses are rapid.

They modify activity of existing intracellular enzymes via second messengers; no new protein synthesis needed.

Major organ systems that clear hormones from circulation

Liver (metabolic degradation) and kidneys (excretion in urine).

Half-life comparison: ADH vs thyroid hormone

ADH (peptide) minutes; thyroid hormone (hydrophobic) days to weeks.

Prolactin illustrates what concept about hormone evolution?

Same hormone can acquire different functions in different vertebrate groups (e.g., milk production in mammals, osmoregulation in fish).

What is the hypothalamo-hypophyseal (pituitary) portal system?

Blood vessel network linking hypothalamic capillaries to anterior pituitary capillaries for hormone transport.

Which lobe of the pituitary receives hormones via the portal system?

Anterior pituitary (adenohypophysis).

Which lobe of the pituitary mainly consists of neurosecretory axon terminals?

Posterior pituitary (neurohypophysis).

How does the hypothalamus regulate the anterior pituitary?

Secretes releasing or inhibiting hormones into the portal blood that stimulate or suppress specific anterior-pituitary cells.

How does the hypothalamus control the posterior pituitary?

Action potentials in hypothalamic neurosecretory neurons trigger direct hormone release (e.g., ADH, oxytocin) from axon terminals into blood.

Name two classic hypothalamic releasing hormones.

Thyrotropin-releasing hormone (TRH) and corticotropin-releasing hormone (CRH).

Give an example of hormone cross-talk between systems.

Neuronal stress signal → hypothalamus → CRH → anterior pituitary → ACTH → adrenal cortex → cortisol (endocrine) for long-term stress.

Why is epinephrine's effect tissue-specific (heart vs intestine)?

Different target cells have different receptor subtypes and intracellular pathways, leading to distinct responses.

Definition of fenestrated capillary and its endocrine significance

Capillary with pores that enhance exchange; abundant around endocrine glands to speed hormone uptake and release.

What is clonal propagation in T-cell biology?

Cytokine-induced rapid division of activated T cells, expanding the population specific to the encountered antigen.