System integration
All organisms use multiple systems to perform the various functions of life. Within these systems there are interdependent sub systems that work together to perform an overall function. At every level in the functioning of an organism, there must be coordination between and within systems. This is achieved by system integration.
System integration depends on effective communication between components so they can interact. The interactions may be simple as negative or positive feedback between two components. More commonly however, they are complex and multifactorial, with many loops and branches. Comparisons can be made with system integration in engineering projects or software design.
Cells
Cells within a multicellular organism interact with each other at multiple levels in a hierarchy of organisation
Tissues
Cells within multicellular organisms are specialised to perform specific functions. Their structure is adapted to their function. Once cell by itself cannot usually carry out its function on a large enough scale to meet the needs of the organism. Instead the organisms use groups of cells of the same type to carry out a function. These groups of cells are called tissues. Large organisms tend to have more cells in each tissue rather than large cells because of surface area to volume issues.
Tissues may contain two or more cell types which specialise for different aspects of the function of the tissue. For example the epithelium that forms the wall of alveoli in lungs has two types of cells. The alveolar type one that make up 95% of respiratory surface that are extensive but very thin allowing for the diffusion of gases. While alveolar type 2 are cuboidal with a dense cytoplasm and they secrete a surfactant that prevents the collapse of alveoli.
The cells in a tissue adhere to each other. Plant cells do this with a middle lamella between the cell walls that is rich and glue pectin. Animal cells use transmembrane proteins that form strong links between neighbouring cells. If blood is regarded as a tissue, it is unusual because blood cells do not stick together.
Cells within tissue communicate with each other and they also communicate with cells elsewhere in an organism.
Organs
An organ is a group of tissues in an animal or plant that work together to carry out a specific function of life. The tissues within an organism are interdependent for example within a leaf the spongy mesophyll is adapted for gas exchange, but it depends on the concentration gradient of carbon dioxide and oxygen which are created by the photosynthesis in the palisade mesophyll. This. Palisade mesophyll tissue is adapted for photosynthesis and it depends on the spongy mesophyll for a supply of carbon dioxide and for removal of oxygen.
Organ systems
Groups of organs interact with each other to perform an overall function of life these groups are known as organ systems. In humans 11 organ systems are recognised.
1. Circulatory system.
2. Digestive system.
3. Endocrine system.
4. Gas exchange system.
5. Intergumentary system.
6. Lymphatic system.
7. Muscular system.
8. Nervous system.
9. Reproductive system.
10. Skeletal system.
11. Urinary system.
In most cases, the organs in an organ system are physically linked for example the digestive and nervous systems. In other cases the organs are dispersed around the body for example the endocrine system.
Organisms
An organism is a living individual made up of interconnected parts. Organ systems composed of organs made up of tissues with constituent cells. These parts are interdependent of failure of a single group of cells in a tissue can cause an organism to die.
The parts of an organism interact and integration of body systems results in a merge of properties for example a cheetah is effective predator. However, this might be difficult to predict if each other component is studied separately. To understand the emergent properties of an organism you must consider systems as a whole.
Hormonal signalling
Hormonal signalling is a chemical signal that is transmitted in the bloodstream. The destination of the signal is widespread to all parts of the body that are supplied with blood but only certain cells respond. These cells are called target cells and they are in any type of tissue. The type of response can be:
- Growth
- Development, including puberty
- Reproduction, including gamete production and pregnancy
- metabolic rate and heat generation
- Solute concentrations in blood, including glucose and salts
- Mood, including stress, thirst, sleep/wakefulness and sex drive
The speed of the response is slower than nervous signalling but the duration of the response is long until the hormone is broken down
Nervous signalling
Nervous signalling is electrical, by passage of cations across membranes. it happens in neurons. The destination of the signal is highly focused to one specific neuron or group of effector cells. These cells are usually muscles or glands. The type of response is can be divided by two categories. One being response due to contraction of muscle:
- striated muscle causing locomotion
-Smooth muscle causing for example, peristalsis and sphincter opening and closing
- Cardiac muscle causing heart rate
Then there are the responses or secretions that come from a gland:
- Exocrine glands for example, sweat or saliva secretion
- Endocrine glands for example epinephrine secretion
These responses are very rapid but short unless nerve impulses are sent repeatedly
Circulatory system in substance suppliance
Materials and energy are transported between organs by the circulatory system. All organs of the body are served by the system, with blood circulating through almost all tissues. Living cells need a constant supply of energy, provided by cell respiration. Cells therefore require a respiratory substrate, commonly glucose and oxygen Assuming that respiration is aerobic. The bloodstream supplies both these substances along with water and carbon compounds needed for growth or repair. It also removes waste products including carbon dioxide produced in respiration.
The brain
The brain is the central integrating organ of our body. It receives information, processes it, store some of it and send instructions to all parts of the body to coordinate life processes. The information received by the brain comes from sensory receptors, both in specialised sense organs such as the eye and also from receptor cells in other organs.
The brain can store information for short term or long-term and sometimes for the rest of life. The capacity to store information is called memory it is essential for learning. Processing of information leads to decision-making by the brain. This may result in signals being sent to muscles or glands, which caused these organs to carry out a response.
The spinal cord for unconscious processes
The nervous system is made up of the central nervous system and nerves that connect the central nervous system to other organs in the body. There are two organs in the central nervous system which are the brain and the spinal cord. The spinal cord is located inside the vertebral column called the backbone. It is widest at its junction with the brain and tapers going downwards towards the pelvis. Pairs of spinal nerves branch off to the left and right between the vertebrae. In humans there are 31 pairs of spinal nerves, each serving a different region of the body.
The spinal cord has two main tissues :
1. White matter containing myelinated axon and other nerve fibres, which convey signals from sensory receptors to the brain and from the brain to the organs of the body
2. Gray matter containing the cell bodies of motor and neurons and neurons, with many synapses between these neurons
Synapses in the grey matter are used for processing information and for decision-making so the spinal cord is also an integrating centre. The spinal cord only coordinates unconscious processes, especially reflexes, in some cases it can do this more quickly than if signals were conveyed to and from the brain.
Unconscious processes
They are performed when awake or asleep, they are performed in voluntarily meaning we do not have to think about the actions and cannot prevent them through thought. Secretion by glands and contraction of smooth muscle are unconscious and therefore involuntary. They are coordinated by the brain and spinal cord.An example is swallowing food once it has entered the oesophagus and vomiting when stomach contents are regurgitated.
Conscious processes
Conscious processes are only performed when awake and are performed voluntarily meaning we think about the action and decide whether or not to carry it out. Contraction of striated muscle can be done consciously and is there for voluntary. It is coordinated only by the cerebral hemispheres of the brain. An example is the initiation of swallowing when food is pushed from the mouth cavity into the pharynx.
Examples of mixed conscious actions
Created muscle can be controlled consciously or unconsciously, for example we consciously choose to stand up and use straight muscles for this action but the unconscious postural reflexes that keep a standing use the same muscles. When a sleep in bed we might turn over unconsciously but we use straight muscles to do this.
Input through sensory neurons
Changes in the external environment can act as stimuli to the nervous system, if perceived by sensory receptors. These receptors are located in the skin and sense organs. Nerve endings of some sensory neurons act as receptors for touch and heat other stimuli are perceived by specialised receptor cells that pass impulses to sensory neurons for example light sensitive rod and cone cells in the retina of the eye.
There are also receptors inside the body that monitor external conditions. Stretch receptors and star and muscles since the state of contraction allowing the brain to deduce the posture of the body. Stretch receptors in the walls of arteries give a measure of blood pressure. Chemo receptors in the walls of blood vessels detect with concentration of oxygen, carbon dioxide and glucose are low or high.
Signals from all receptor cells and from nerve endings that perceived stimuli directly are conveyed to the central nervous system by censoring neurons. The signals are in the form of nerve impulses carried along the axon of sensory neurons. These axon is very length depend depending on the distance between the receptor cell and the brain or the spinal cord. They might be a meter or more in length if for example the receptor cells at the end of a toe.
The brain receives all the signals from the main sense organs located in the head. These are the eyes, ears, nose, and tongue. The spinal cord receives signals from other organs of the body including skin and muscles. Sensory inputs to the brain are received by specialised areas in the cerebral hemispheres. For example, the visual cortex that receives signals from road and cone cells in the posterior part of the cerebrum.
Axon of sensory neurons enter either the spinal cord through one of 13 pairs of spinal nerves or the brain by one of the 12 pairs of cranial nerves. For example signals from rotten cones in the eyes enter the brain via the left or right optic nerve and signals from the ear enter via the vestibulocochlear nerve.
Controlling muscles through motor neurons
The cerebral hemispheres of the brain have a major role in the control of striated muscles and certain glands. In particular, the primary motor cortex and signals via motor neurons to each striated muscle in the body. Striated muscle is attached to bone. It is used for locomotion and controlling posture and can be controlled consciously.
The signals in motor neurons are nerve impulses. The cell body and dendrites of many motor neurons are located in the great matter of the cerebral hemispheres. Typically there are many dendrites, receiving signals from different relay neurons and transmitting them to the cell body. One axon leads from the cell body out of the brain and down the spinal cord. There it forms a synapse with a second motor neuron, whose axon leads to one specific straight muscle. The axon is in these two motor neurons may in total extent to a meter or more depending on the location of the muscle. The axons of motor neurons are bundled up in nerves, often together with the axons of sensory neurons. When a nerve impulse reaches the end of the axon, it stimulates the muscle fibres to contract and gland cells to secrete.
Nerves
A nerve is a bundle of nerve fibres enclosed in a protective sheath. Nerves very in size depending on the number of nerve fibres and the proportion of them that are myelinated. The widest is the sciatic nerve, which is approximately 20 nm across. The optic nerve is estimated to contain between 770,001.7 million nerve fibres. Small nerves may contain fewer than 100 fibres.
Most nerves contain nerve fibres in both sensory and motor neurons. However, some contain only sensory neurons and some contain only motor neurons. All organs of the body are served by one or more nerves.
reflexes
A reflex action is a rapid involuntary response to a specific stimulus . Reflexes are the simplest type of coordination is by the nervous system, as the signals pass through the smallest number of neurons. This helps to speed up reflexes, which is an advantage of the response prevents harm to the body.
Some reflex actions are coordinated by the spinal cord such as the pain reflex when we left our foot after treading on a sharp object. Other reflexes are coordinated by the brain for example constriction of a pupil in the eye in response to bright light, which protects the retina from damage. Reflexes depend on parts of the nervous, skeletal and muscle systems Working together.
- Receptors
Receptor cells since a change in conditions, known as stimulus. Each receptor cell detects only one type of stimulus. The nerve endings of some sensing neurons can perceives a stimulus directly so there is no need for a separate receptor cell. Pain and heat or detected in this way by nerve endings in the skin. - Sensory neurons.
Sensory neurons receive signals, either from receptor cells or from their own sensory nerve endings, and pass them to neurons in the central nervous system. To do this, they have a long axon that carry nerve impulses from the receptor to the spinal cord or brain. These axons end at synapses with interneurons in the grey matter of the spinal cord or brain. Grey matter is a tissue containing many cell bodies of inter neurons and motor neurons. - Interneurons.
These cells are located inside the central nervous system. They typically have many branched fibres called dendrites, along which nerve impulses travel. Inter neurons process signals brought by sensory neurons and make decisions about appropriate responses. They do this by combining impulses from multiple inputs and then passing impulses to specific other neurons. The decision-making process that results in a reflex action is very simple because there may be only one interneuron connecting a specific sensory neuron to the motor neuron that can cause an appropriate response. - Motor neurons
Motor neurons receive signals via synapses with neurons. If a threshold potential is achieved in a motor neuron, and impulses passed along the axon which leads out of the central nervous system to an effector. The axon does not change his position or connections, so the impulse always travels to the same effector cell or small group of effector cells. - Effectors
These carry out the response to a stimulus when they receive a signal from a motor neuron. There are two types of effectors:
- Muscles responded by contracting. For example, muscles in the leg contract to lift the foot off a sharp object.
- Gland responding. For example, the smell of food may cause glands in the head to secrete saliva.
A reflex arc is a sequence of cells that participate in coordination of a reflex. If the stimulus is P pain or heat, nerve endings of the sensory neuron act as the receptor, rather than specialised receptor cells.
The cerebellum
The cerebellum has important roles in the control of skeletal muscle contraction and balance. It does not make decisions about which muscles will contract but it fines the timing of contractions. It allows very precise coordination of movements and help helps us to maintain posture, for example when we are standing. It also helps us with activities requiring motor memory, such as writing a bike or typing on a keyboard.
The circadian rhythm
Humans are adapted to live a 24 hour cycle and have rhythms and behaviour that fit this cycle they are known as circadian rhythms. These rhythms can continue even if a person has placed experimentally and continuous light or darkness, because they are controlled by an internal system.
Circadian rhythms in humans depend on two groups of cells in the hypothalamus called the suprachiasmic nuclei. These cells set and follow a daily rhythm even when grown in a vitro culture, with no external cues about the time of day. In the brain, they control the secretion of the hormone melatonin by the pineal gland. Melatonin secretion increases in the evening and drops to a low level at dawn. As a hormone is rapidly removed from the blood by the liver, blood concentrations rise and fall rapidly in response to these changes integration.
The most obvious effect of melatonin is the sleep wake cycle. High melatonin levels cause feelings of drowsiness and promote sleep through the night. Following levels of melatonin encourage waking at the end of the night. Experiments have shown melatonin contributes to the nighttime drop in core body temperature . Blocking the rise in melatonin levels at night reduces how much temperature drops, and giving melatonin artificially during the day cause a drop in core temperature. Melatonin receptors have been discovered in the kidney suggesting that decreased urine production at night maybe another effect of this hormone.
When humans are placed experimentally in an artificial environment with no light cues to indicate the time of day, the suprachiasmic nuclei and pineal gland usually maintain a rhythm of slightly longer than 24 hours. This shows that timing of the rhythm is normally adjusted by a few minutes or so each day so that it is Synchronised with the diurnal cycle. A special type of ganglion cell in the retina of the eye detect light wavelengths of around 460 to 480 nm and passes impulses to cells in the suprachiasmic nuclei. This signals the suprachiasmic nuclei the timing of dusk and dawn and allows it to adjust melatonin secretion so that corresponds to the day night cycle.
Epinephrine secretion
Epinephrine, also called adrenaline, is a hormone that prepares the body for vigourous physical activity. It is secreted by the adrenal glands. when epinephrine reaches tissue where it has an effect, it binds to adrenogenic receptors in the plasma membrane of target cells. This triggers responses inside these cells.
Epinephrine has effect on most tissues. A common theme among the responses is preparation for vigourous physical activity. In particular, epinephrine increases the supply of oxygen and glucose of skeletal muscles, maximising their production of ATP by respiration:
- muscle cells breakdown glycogen into glucose, which can be used in aerobic or an aerobic respiration.
- Liver cells also break down glycogen into glucose which is released into the bloodstream.
- Bronchi and bronchioles dilate due to relaxation of smooth muscles, so the airways become wider and ventilation is easier.
- The ventilation rate increases so a larger volume of air is breathed in and out per minute.
- The sinoatrial node speeds up the heart rate, so cardiac output increases
- arterioles that carry blood to muscles and to the liver widen due to relaxation of smooth muscle cells causing via vasodilation, so more blood flows to them.
- arterioles that carry blood to the gut, kidneys, skin and extremities become narrower due to the contraction of smooth muscle cells causing vasoconstriction, so less blood flows to them.
As a result of these responses, the skeletal muscles used during vigourous activity receive a greater volume of blood per minute and this blood carries more glucose and oxygen.
This secretion of epinephrine in the adrenal glands is controlled by the brain. It increases when vigourous activity may be necessary because of a threat or an opportunity. For this reason, epinephrine is known as the fight or flight hormone. In the past, when humans were hunters And gatherers rather than farmers nephron would’ve been secreted when they were hunting for prey or were threatened by a predator. In the modern world, many athletes use pre-race routines to stimulate up an effort secretion so their heart rate is already increased when vigourous physical activity begins.
The hypothalamus and pituitary gland
The hypothalamus is a small region in the brain that has major roles in the integration of body systems. It consists of a thin wall of tissue located on the left and right side of the third ventricle and below. Ventricles are spaces inside the brain that are filled with cerebral spinal fluid. The hypothalamus links the nervous system to the endocrine system via the pituitary gland.
Within the hypothalamus there are specialised areas called nuclei. Each nucleus operates one or more specific control systems, using information from a variety of sources. Some nuclei have sensors for blood temperature, blood glucose concentration, osmolarity and the concentration of various hormones. Many nuclei receive signals from sense organs, either directly or indirectly via the cerebral hemispheres. There are also inputs from other parts of the brain, such as the medulla oblongata, the hippocampus and the amygdala.
There are close relationships between the hypothalamus and the pituitary gland, which are located directly below it and connected by a narrow stock. The pituitary gland has two distinct parts: the anterior lobe and the posterior lobe. These two lobes operate in different ways, but both of them secrete hormones into blood capillaries under the direction of nuclei in the hypothalamus.
Osmo regulation and puberty or two processes based on system integration by the hypothalamus and pituitary gland.
- Osmo receptors in the hypothalamus constantly monitor the solute concentration of the blood. This and other inputs influence how much antidiuretic hormone is produced by the neurosecretory cells in the hypothalamus. The axon is in the neuro secretary cells transport the antidiuretic hormone to the pituitary gland, where it is secreted into blood capillaries.
- The hypothalamus initiates puberty by secreting GNRH, a neuro hormone that stimulates the secretion of luteinising hormone and follicle stimulating hormone by the pituitary gland. These hormones in intern stimulate the secretion of testosterone and males and oestradiol and progesterone in females, leading to changes associated with puberty.
Turn on secreted from the pituitary gland
The anterior pituitary gland secretes:
- Human growth hormone
-Thyroid stimulating hormone
- Luteinizing hormone
- Follicle stimulating hormone
- prolactin
The posterior pituitary secretes:
- Antidiuretic hormone
- Oxytocin
Feedback control of heart rate
The sinoatrial note is a special group of cardiac muscle cells in the wall of the right atrium. It acts as a pacemaker for the heartbeat. The pacemaker receives signals from the cardiovascular centre in the medulla oblongata of the brain. These signals reached the pacemaker via branches of two nerves:
- Signals from the sympathetic nerve caused the pacemaker to increase the frequency of heartbeats. And healthy young people, the heart rate can increase to 3 times the resting rate.
- Signals from the vagus nerve cause a pacemaker to decrease the heart rate.
The cardiovascular centre receives sensory input from baroreceptors in the walls of the aorta and carotid arteries, which monitor blood pressure. This allows control of blood pressure by negative feedback. The response to low blood pressure is an increase in heart rate, which increases blood pressure. The response to high blood pressure is a decrease in heart rate, which reduces blood pressure.
The cardiovascular Centre also receives sensory input from chemo receptors in the aorta and carotid arteries. Some chemo receptors monitor blood oxygen concentration and others monitor pH, which berries with carbon dioxide concentration. Negative feedback is again used as the method of control. Low oxygen concentration and low pH cause the heart rate to speed up, increasing blood flow to the tissue so more oxygen is delivered and more carbon dioxide is removed. High oxygen concentration and high pH cause the heart rate to slow down.
The sinoatrial node also respond to epinephrine in the blood, by increasing the heart rate. This happens when the Amla sends distressed signals to the hypothalamus, which sends signals directly via nerve fibres to the cells in the adrenal gland that secrete nephron. Epinephrine can override the normal feedback control mechanisms while the body response to a threat.
