Course Content
KCP 1 – Obesity (Lectures)
This covers all the lecture content from the key clinical problem "Obesity" for cellular response 3.
Cellular Response 3
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Learning outcome 1.Define homeostasis and explain its significance


  • Refers to the regulation of physiological variables to maintain a stable and balanced internal environment.
  • Variables include body temperature, blood glucose levels, and fluid balance.
  • Maintained through a complex network of feedback mechanisms.
  • Sensors detect changes and effectors respond to restore balance.
  • Goal is to maintain stability in the internal environment, allowing for adaptation to changing external conditions and survival.

Learning outcome 2.Define homeostatic mechanism and give 3 examples

Homeostatic mechanism:

A process in which a biological system maintains a stable internal environment, by making adjustments to respond to changes in external conditions. The mechanism operates through a complex network of feedback loops that include sensors to detect changes, and effectors to restore balance.

Homeostatic Mechanisms: There are three components that contribute to maintaining homeostasis in an organism:

  • The Nervous System: The Quick Component (Systemic)

  • The Endocrine System: The Slow Component (Systemic)

  • Behavioural Responses. Examples of behavioural responses include curling up and wearing warm clothes in response to cold and resting in shades and fanning in response to heat, which play a role in temperature homeostasis.

Learning outcome 3.Define negative feedback and explain its role in homeostasis giving  3 examples

Negative Feedback Mechanism:

Negative Feedback is a process where changes in the internal environment are detected and regulated by a complex network of feedback mechanisms to maintain stability and balance. The end goal is to maintain homeostasis and enable the organism to adapt to changing external conditions.

There are three levels at which negative feedback occurs:

  • Molecular Level: The end product regulates its own concentration by inhibiting the enzyme responsible for its production. Examples include the regulation of glucose concentration in the blood and the regulation of T4 hormone levels.

  • Cellular Level: The local potential in the neuron depolarizes, causing ionic changes that trigger repolarization, which returns the membrane potential to its resting value.

  • Systemic Level: Negative feedback mechanisms occur at the endocrine and nervous system levels. Endocrine regulation, such as the regulation of plasma glucose levels by insulin hormone, and nervous regulation, such as the baroreceptor reflex arc, maintain stability and balance in the internal environment.

Learning outcome 4.Define positive feedback and explain its role in normal and failed homeostasis giving examples

Positive Feedback in Physiology: Positive feedback operates in physiological processes that require rapid and substantial changes. Examples include:

  • Generation of an action potential

  • Ovulation

  • Parturition

While these processes may seem unrelated to homeostasis, they play an indirect role in maintaining stability within the internal environment. For example, positive feedback generates nerve impulses that are essential for the nervous system to carry out its homeostatic functions.

However, positive feedback can also play a role in cases where homeostasis fails and body functions rapidly deteriorate. For example, in a massive haemorrhage, positive feedback can exacerbate the situation.

Learning outcome 5.List the components of a reflex arc in relation to homeostasis

The components of a reflex arc in relation to homeostasis are:

  • Receptor: detects changes in the internal or external environment and sends sensory signals to the central nervous system.

  • Sensory Neuron: carries the sensory signals from the receptor to the central nervous system.

  • Integrating Center: the central nervous system, usually the spinal cord or brain, processes the sensory signals and decides the appropriate response.

  • Motor Neuron: carries the response from the integrating center to the effector.

  • Effector: the muscle or gland that carries out the response to restore homeostasis.

  • Feedback Mechanism: a mechanism that monitors the effect of the response and sends feedback to the integrating center to adjust the response as necessary.

Learning outcome 6.Compare the general roles of the nervous and endocrine systems in homeostasis

The Nervous System and Endocrine System: Essential for Homeostasis

The nervous system and endocrine system are two important systems in the body that work together to maintain homeostasis. They both play critical roles in regulating the internal environment and responding to changes. However, they differ in their functions and responses.

The Nervous System

  • Responsible for rapid, short-term responses
  • Uses electrical signals to transmit information
  • Results in immediate changes in muscle or gland activity
  • Restores balance quickly

The Endocrine System

  • Releases hormones into the bloodstream
  • Acts on specific target cells to regulate physiological processes
  • Hormonal changes may take several minutes or hours to have an effect
  • Sustains response for a longer period compared to the nervous system

In conclusion, both systems work in harmony to maintain homeostasis with the nervous system providing quick responses and the endocrine system providing sustained responses.

Learning outcome 7.Define circadian rhythm and give 2 examples

Circadian rhythm is the natural biological process that regulates the sleep-wake cycle, hormone secretion, and other physiological functions in living organisms, including humans, with a 24-hour cycle. This internal “biological clock” is influenced by environmental cues such as light and dark, and helps to coordinate and synchronize physiological processes with the daily cycle of day and night.


  • Sleep-Wake Cycle: Circadian rhythm helps regulate the sleep-wake cycle, ensuring that individuals feel alert and awake during the day and drowsy and ready for sleep at night.

  • Hormone Secretion: The circadian rhythm also regulates the secretion of hormones such as cortisol, which helps regulate the body’s response to stress, and melatonin, which helps regulate the sleep-wake cycle.

Learning outcome 8.Describe the location and basic structure and function of the endocrine glands

The endocrine glands are a group of glands that secrete hormones into the bloodstream to regulate various physiological processes in the body. These glands are located throughout the body and include:

  • Pituitary gland: Located at the base of the brain and referred to as the “master gland,” it regulates the activity of other endocrine glands.

  • Thyroid gland: Located in the neck, it produces hormones that regulate metabolism, growth, and development.

  • Adrenal glands: Located atop the kidneys, they produce hormones that regulate the body’s response to stress, including cortisol and adrenaline.

  • Pancreas: Located in the abdomen, it produces hormones, such as insulin and glucagon, that regulate blood sugar levels.

  • Ovaries (in females) and testes (in males): These reproductive glands produce hormones that regulate the menstrual cycle and fertility.

  • Parathyroid glands: Located near the thyroid gland, they produce a hormone that regulates calcium levels in the blood.

The basic structure of endocrine glands typically includes cells called endocrine cells or glands, which secrete hormones into the bloodstream. These hormones then travel to target cells or tissues, where they bind to specific receptors and trigger a response that helps regulate physiological processes such as growth, metabolism, and reproductive functions

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