1. Three layers (tunics) that form the wall of the eyeball 2. Optical components admit and focus light 3. Neural component:

Lecture #3 Flashcards by caroline charteris

Vision (sight)

perception of objects in the environment by means of light they emit or reflect

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Light =

visible electromagnetic radiation
Human vision: wavelengths 400 - 700 nm
UV radiation: < 400 nm; too much energy
Infrared radiation: > 700 nm; too little energy

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Anatomy of the Eye

Three layers (tunics) that form the wall of the eyeball
Optical components admit and focus light
Neural component:

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Fundus of the eye

Macula lutea -fovea centralis
• Pit in center
• Produces most finely detailed images

Optic disc
No photoreceptor cells
• If image falls on this area cannot be seen = blind spot

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Iris diameter controlled by contractile elements

Parasympathetic - narrows pupil

Sympathetic - widens pupil

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Pupillary constriction and dilation occurs:

When light intensity changes

2. When gaze shifts between distant and nearby objects

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Photopupillary reflex

pupillary constriction in response to light

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Emmetropia

normal eyesight fixed on an object >6m away

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hyperopia

farsighted – cannot see nearby

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Myopia

(nearsighted) – Cannot see distance

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Sensory Transduction

Retina converts light energy into action potentials

Rods,cones,and certain ganglion cells

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Photoreceptor cells

absorb light and generate a chemical or electrical signal

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Rod (photoreceptor) Cells

night vision or monochromatic vision

rhodopsin + cannot distinguish colour

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Cone (photoreceptor) Cells

day or colour (trichromatic) vision

Photospin + can absorb colour

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Outer Segment (photoreceptor cell)

Specialized to absorb light

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Dark

Light

In DARK, rods steadily release the glutamate = DARK CURRENT

Rods absorb LIGHT 􏰀 stops glutamate

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Principal Mechanisms of communication between cells

Gap Junctions
Neurotransmitter
Paracrine - secreted into tissures
Hormones - chemical messengers travel in bloodstream

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Endocrine system

glands, tissues, and cells that secrete hormones

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Endocrinology

organs that are traditional sources of hormones

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Hormones

chemical messengers that are transported by the bloodstream

Target organs or cells

those organs or cells that have receptors for a hormone and can respond to it

Peptide Hormones

hydrophilic
cannot penetrate target cell
bind to surface receptors and activate IC processed

Steroid Hormones

Hydrophobic
penetrates plasma membrane and bind to internal receptors
influence gene expression
takes several hours or days

Hormone Interactions

most are sensitive to >1 hormone = interactive effects

Synergistic Effects

Multiple hormones act | together for greater effect

Permissive effects

One hormone enhances the | target organ’s response to a second later hormone

Antagonistic effects

One hormone opposes the | action of another

Hypothalamus

forms floor and walls of third ventricle of brain | regulates primitive functions, but many are carried out by pituitary gland

Hypothalamic Hormones

there are 8 hormones produced in the hypothalamus 6 inhibit the anterior pituitary 2 are released into capillaries in the posterior pituitary

Posterior Pituitary Hormones

- nerve tissue not a true gland example oxytocin and ADH

Negative Feedback

increase target organ hormone levels which inhibits the release hypothalamic and/ or pituitary hormones

Growth Hormone

- many effects on the body | - liver produces insulin-like growth factors

Hyper-secretion

Gigantism

Hypo-secretion

Pituitary Dwarfism

Thyroid Gland

largest endocrine gland has 2 lobes secretes T4, T3 in response to TSH Secrete calcitonin

Thyroid Disorders

Decreased TH at birth (congenital hypothyroidism) Decreased Th at adult (Myxedema) Goiter - enlarged thyroid gland

The Adrenal Medulla

- secretes norepinephrine and epinephrine | - increases alertness and prepares the body for physical activity

Mineralocorticoids

regulates electrocyte balance | stimulates Na and K

Glucocorticoids

Regulates metabolism, helps the body adapt to stressors | secretes in response to ACTH

Sex Steroids

Androgens: male development

Adrenal Disorders

Cushing syndrome - excess cortisol secretion, lots of fat ``` Adrenogenital syndrome (AGS) enlargement of sexual organs, maculating effects on women ```

The Pancreatic Islets

1-2 million islets - clusters of endocrine cells that secrete hormones that regulate glycemia (blood sugar)

Glucagon

secreted by alpha a cells released between meals b/c of falling blood glucose In liver: stimulates release of glucose Adipose tissue: stimulates the release of fatty acids

Insulin

secreted by Beta cells released after a meal when blood glucose is raising stimulates cells to absorb nutrients, store and metabolize

Diabetes Mellitus

Most prevalent metabolic disease in the world | • Disruption of metabolism due to hyposecretion or inaction

Diabetes Pathogenesis

cells cannot absorb glucose fat catabolism increases free fatty acids and ketones in the blood chronic hyperglycemia

Type 1 Diabetes Mellitus

5-10% of cases insulin insufficiency inherited

Type 2 Diabetes Mellitus

90-95% insulin resistance aka failure to respond to insulin risk factors heredity, age, obesity, ethnicity